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Geology Memoirs 

Published by Field Museum of Natural History 






JUNE 29, 1973 q^ 




.V of °>^ N 

,.S NATURAL °^\ 





Geology Memoirs 

Published by Field Museum of Natural History 


Chairman, Department of Geology 
Field Museum of Natural History 

Jersey City, New Jersey 

JUNE 29, 1973 

Patricia M. Williams 
Managing Editor, Scientific Publications 

Library of Congress Catalog Card Number: 73-79270 




Abstract ix 

Introduction 1 

List of Stratigraphic Black Shale Horizons and Localities 3 

Systematic Descriptions 6 

Order Iniopterygia, nov 6 

Family Iniopterygidae, nov 6 

Genus Iniopteryx, nov 6 

Iniopteryx rushlaui, sp. nov 6 

Iniopteryx tedwhitei, sp. nov 21 

Genus Promexyele, nov 22 

Promexyele peyeri, sp. nov 22 

Promexyele bairdi, sp. nov 31 

Family Sibyrhynchidae, nov 35 

Genus Sibyrhynchus, nov 35 

Sibyrhynchus denisoni, sp. nov 35 

Genus Iniopera, nov 45 

Iniopera richardsoni, sp. nov 46 

Genus Inioxyele, nov 60 

Inioxyele ickitei, sp. nov 60 

Comparative Anatomical and Phylogenetic Significance of the Iniopterygia 64 

References 67 



An entirely new group of Pennsylvanian fishes, be- 
longing to the class Chondrichthyes, is described and 
their comparative anatomical and phylogenetic rela- 
tions are discussed. Seven species belonging to five 
genera are distinguished and placed within the subclass 
Holocephali as a separate order, Iniopterygia. The 
iniopterygians are structural, but not phyletic, inter- 
mediates between the chimaeroids (as here denned) and 
the elasmobranchs. Present analysis permits the no- 
tion that the holocephalians and the elasmobranchs are 

sister groups sharing a common ancestor that never 
possessed a bony dermal armor but an even spread of 
lepidomorial denticles over the entire skin and the sto- 
modaeum. Iniopterygians and chimaeroids, in turn, 
appear to be sister groups having evolved from a com- 
mon ancestor that combined an autostylic jaw sus- 
pension with a generalized shark-like dentition. 

Iniopterygians are presently known only from car- 
bonaceous, sheety shales of the Pennsylvanian basin 
complex of central North America. 



Since 1954 when E. S. Richardson, Jr., and the senior 
author began an intensive study of the carbonaceous, 
sheety, black shales that overlie coal III-A in Parke 
County, Indiana (Mecca Quarry shale), it was quite 
obvious that among the hundreds of fish remains recov- 
ered from this deposit there were peculiar cartilaginous 
fishes clearly not identifiable as sharks. The head re- 
gion and the post-cranial skeleton of these peculiar 
vertebrates consist of calcified cartilage and the denti- 
tion is made up of a considerable variety of teeth, some- 
times fused into labio-lingual tooth whorls. Also, in 
some genera the mouth cavity is armored with large 
plates that consist of numerous, fused denticles. 

As all specimens had been mutilated by predators 
(see Zangerl and Richardson, 1963) and therefore do 
not consist of skeletons in pristine condition, the mor- 
phology of these fishes remained a mystery for many 
years, in spite of the fact that more than a hundred 
specimens were at hand. Even those specimens that 
seemed to be relatively complete (and have since proved 
to be so) seemingly failed to fit into the structural plan 
of any primitive vertebrates presently known. For 
want of an identification and because they had tuber- 
culated head plates, we called them "placoderms." 

In the meantime, the junior author began to collect 
vertebrates from carbonaceous, sheety, black shales in 
Iowa and Nebraska. In the latter state he enjoyed the 
co-operation of local amateur collectors, primarily Mr. 
W. D. White and Mr. William Rushlau, both of Omaha, 
Nebraska. This collecting activity resulted in the pres- 
ervation of numerous very important specimens includ- 
ing a variety of sharks and also the curious questionable 
vertebrates. In the fall of 1969 the junior author in- 
vited Dr. Barbara Stahl and the senior author to his 
home where he displayed his collection of vertebrates 
from several black shales of Iowa and Nebraska. A 
number of these skeletons resembled the "placoderms" 
of the Mecca fauna, although most of them did not 
display tooth whorls or large tuberculated plates. In 
contrast to the material from Indiana, these specimens 
did not appear to have been preyed upon and seemed to 
be in fair to excellent state of articulation. It was Dr. 
Stahl who broke the riddle by her observation that in 
several specimens (preserved in side view) the large, 
evidently paired fins just back of what appeared to be 

the head region, seemed to lie consistently on the dorsal 
side of the vertebral column and that they seemed to 
extend from the "nape" of the neck. The senior author 
then reviewed all of the best specimens from the Indi- 
ana localities and found that the dorsal position of the 
anterior paired fins is indeed evident in all laterally en- 
tombed individuals in which this region of the skeleton 
has been left undisturbed. It also became quite evident 
that many of the Indiana skeletons were more complete 
(and less disturbed) than had been assumed prior 
to the examination of the junior author's collection. 
An earlier suspicion that the material included not one, 
but several kinds of these peculiar fishes became in- 
creasingly apparent as the study of the material pro- 
gressed. It was imperative that the junior author's col- 
lection of iniopterygians be studied along with the 
material from Indiana and he has graciously donated it 
to Field Museum. At the same time field work in 
Indiana, especially in the roof shale over coal IV-A in 
Pike County, Indiana, has furnished a large number of 
additional specimens. 

The following account will provide a broad mor- 
phological characterization of a new order of vertebrates 
and the description and characterization of five genera 
and seven species, all of which, peculiarly, have escaped 
the recorded fossil record to date. Because of the na- 
ture of their preservation many aspects of their mor- 
phology remain to be determined in the future as addi- 
tional (especially well-preserved) individuals are col- 
lected, a perfectly realistic hope in view of the fact that 
these animals are extremely abundant in a number of 

The illustrations are the work of G. R. Case, based 
on drawings and sketches by the senior author. Dr. 
Tibor Perenyi, staff illustrator at Field Museum, added 
some finishing touches to the illustrations. 

The following persons have been members of Field 
Museum collecting parties since 1963: Mr. Orville L. 
Gilpin, Miss Gwendolyn Hall, Mr. Arthur R. Zangerl, 
and the senior author. We are also much indebted to 
Mrs. Winifred Reinders for her care with the manu- 
script and to Dr. Eugene S. Richardson, Jr., for the 
critical reading of the text. All radiographs were made 
with Siemens Heliodor-Duplex X-ray equipment fitted 
with a Pantix tube. 














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The following is a list, in stratigraphic sequence from 
youngest to oldest, of the black shales that have pro- 
duced iniopterygians and the localities from which they 
have come. This permits us to avoid the repetitious 
listing of this information for the referred specimens 
listed under each species below. The stratigraphic and 
geographic distribution of the localities is given in Fig- 
ure 1. 

Queen Hill shale, Lecompton formation, Shawnee group, 
Virgil series, Stephanian A, Pennsylvanian. 
Plattsmouth, Nebraska, Cass County, Midwest Con- 
struction Co., Ace Hill E> , SW> 4 SW'., Sec. 33, 
T12N, R14E. 
Stennett, Iowa, Montgomery County; Kaser Con- 
struction Co., Quarry, CNE' 4l Sec. 27, T73 N, 
R38 W. 

Wea Shale, Westerville formation, Kansas City group, 
Missouri series, Westphalian D, Pennsylvanian. 

Papillion, Nebraska, Sarpy County; City Wide Rock 
and Excavation Co. (Hansen quarry, quarry 6), 
halfway between Papillion and Bellevue, Ne- 

braska, on Route 370; SE' 4 NE ! 4 SW 1 .,, Sec. 
32, TUN, R13E (fig. 2). 
Richfield, Nebraska, Sarpy County, City Wide Rock 
and Excavation Co., PWA quarry (also known 
as Schmid quarry), S3 2 N ' 2 Sec. 28, T13N, 
R12E, north of Platte River. 

Stark shale, Dennis formation, Bronson group, Mis- 
souri series, Westphalian D, Pennsylvanian. 

Crescent, Iowa, Pottawattamie County, Schildberg 
Construction Co., quarry, about 2 miles west 
of town, NE} 4 NE% Sect. 34, T76N, R44W 
(Omaha North Quadrangle). 

Ft. Calhoun, Nebraska, Washington County; Ft. Cal- 
houn Rock Products Co., quarry, NWJ4 NW' 4 
SEJ4 Sect. 1, T17N, R12E. 

Papillion, Nebraska, Sarpy County; City Wide Rock 
and Excavation Co. (Hansen quarry, quarry 6), 
halfway between Papillion and Bellevue, Ne- 
braska, on Route 370; SEM NEM SWJ4, Sec. 
32, T14N, R13E. 

La Platte, Nebraska, Sarpy County; City Wide Rock 
and Excavation Co., quarry (Iske quarry), River 


Westerville Is. I 
Wea shale ■ 

«*** m ' ■ ■ ""* » * 

Winterset Is. 

Stark shaie 
Canville \ Dennis Is. 

Bethany Falls Is. 
(below water) 

Fig. 2. City Wide Rock and Excavation Co., Hansen quarry, June 1969. Wea shale exposed in headwall between Westerville lime- 
stone (above) and Winterset limestone beneath. Stark shale is almost at water level. 



Fig. 3. Penn-Dixie quarry, Winterset, Iowa, April 1968. 
Stark shale exposed in middle foreground. 

Road from Offutt Airbase, SWK SEM SWM 
Sec. 20, T13N, R13E and Nj ■> N> ., NE'/,, Sec. 
29, T13N, R13E. 
Winterset, Iowa, Madison County; Penn-Dixie Ce- 
ment Co. quarry, immediately southeast of town 
limits, W ] 2 Sec. 6, T75N, R27W. (fig. 3). 

Labette black shale, Labette formation, Marmaton 

group, Des Moines series, Westphalian D, Penn- 


Madrid, Iowa, Boone County; exposures of black 

shale along the Des Moines River, about 2.5 

miles NW of Madrid, C NE' 4 Sec. 33, T82N, 

R26W, Preston Branch Tributary of Des Moines 

River (fig. 4). 

Excello shale, (equivalents: black shale over coal IV-A, 
Indiana; black shale over coal IV, Illinois), Car- 
bondale formation, Des Moines series, Westphal- 
ian lower D, Pennsylvanian. 

Barret Cemetery: strip mine headwall, NW }\, Sec. 3, 
T3S, R7W (Augusta quadrangle), north of Bar- 
ret Cemetery, Pike County, Indiana. 

Bethel Church: strip mine headwall, about center o 1 
NW ] 4 of Sec. 3, T3S, R7W (Augusta quad- 
rangle), about ! 4 mile SE of Bethel Church. 
Pike County, Indiana (fig. 5). 

Beaver Pond: strip mine headwall close to boundary 
between NW and SW '4 of Sec. 10, T3S, R7W 
(Augusta quadrangle), about 1 mile south of 
Barret Cemetery, Pike County, Indiana. 

Pit 12, Peabody Coal Co., Grundy County, Illinois. 

Pit lit, Peabody Coal Co., Kankakee County, Illinois. 

Mecca Quarry shale, Liverpool cyclothem (Linton for- 
mation), Des Moines series, Westphalian upper C, 

Mecca quarry: SW % NE h Sec. 29, T15N, R8W, 
about 1 mile from town of Mecca, Wabash 

Township, Parke County, Indiana (Zangerl and 
Richardson, 1963, pp. 28, 44, pi. 1, 2). 

U.S. Highway kl •" outcrop of Mecca Quarry shale 
along U.S. Highway 41, SE of Mecca Quarry 
(Zangerl and Richardson, 1963, p. 44). 

Mine Creek: exposures of Mecca Quarry shale along 
Mine Creek, NE ',, Sec. 29, T15N, R8W, Wa- 
bash Township, Parke County, Indiana (Zangerl 
and Richardson, 1963, pp. 7, 27, 44). 

Montgomery Creek: Wabash Township, Parke 
County, Indiana (Zangerl and Richardson, 1963, 
pp. 27, 39, pi. 5). 

Spencer Creek: Wabash Township, Parke County, 
Indiana (Zangerl and Richardson, 1963, pp. 7, 

West Montezuma: Clay City Pipe Co., Pit no. 3, 
NW 14, Sec. 35, T16N, R9W, Vermillion Coun- 
ty, Indiana (Zangerl and Richardson, 1963, pp. 
40, 58). 

Moorehead's Bank: SW \i SW }i SW %, Sect. 28, 
T17N, R9W, Vermillion County, Indiana 
(Zangerl and Richardson, 1963, pp. 7, 83). 

Arketex: Arketex Ceramic Corp. Pit, SE ',, Sec. 
10, SW i 4 Sec. 11, T16N, R9W, Vermillion 
County, Indiana (Zangerl and Richardson, 1963, 
pp. 7, 63). 

Chinook mine: Ayrshire Colliery, S of Staunton, 
Clay County, Indiana. 

Otter Creek: near bridge of section road over creek, 
Sec. 25 and 30, T30N, R8W, north of Ehrman- 
dale (Richter Cemetery), Vigo County, Indiana. 

Fig. 4. Outcrop of Labette shale, along bank of Des Moines 
River near Madrid, Iowa. 



tfc^lUI*" 11 

Fig. 5. Black shale over coal IVA (Excello shale); Summer 1970; Bethel Church locality, Pike County, Indiana. 

Jelliff: along Court Creek, SW U SW \i Sec. 15, 

TUN, R2E (Galesburg quadrangle), NW of 

Knoxville, Illinois. 

Logan Quarry shale, Lower Wiley cyclothem (Staunton 

formation), Des Moines series, Westphalian upper 

C, Pennsylvanian. 

Logan Quarry: NE ' , SW ' 4 Sec. 9, T16N, R8W, 
Reserve Township, Parke County, Indiana 
(Zangerl and Richardson, 1963, pp. 7, 67, pi. 3). 

Hajji Hollow: NE \ ., SE ' 4 Sec. 5, T15N, R8W, 
Wabash Township, Parke County, Indiana. 


Class Chondrichthyes 

Subclass Holocephali 

Order Iniopterygia, nov. 

Characterization .-Cartilaginous fishes whose skele- 
tons tend to calcify at an early ontogenetic age. Gen- 
eral body habitus similar to modern chimaeroids. Pala- 
toquadrate fused to neuroeranium. Mouth terminal. 
Skin devoid of dermal denticles except in Iniopera. 
Dentition ranging from labio-lingual rows (tooth fam- 
ilies) of individual, extremely simple denticles, to rows 
of individual denticles with side cusplets, to an amazing 
variety of tooth whorls (individuals of tooth families 
fused at their bases) producing a "heterodonty" un- 
rivalled among fishes. Snout sometimes provided with 
tubercles. Mucous membrane denticles in the pharyn- 
geal region of some forms, large plates consisting of 
fused denticles lining mouth cavity of others. Pectoral 
fins large, characteristically attached to the shoulder 
girdle elements near their dorsal ends. Anteriormost 
fin ray of pectoral fin usually enlarged in males, bearing 
sharp denticles. Pelvic fins much smaller than pectoral 
fins and consisting of short cartilage rays followed dis- 
tally by ceratotrichia (so far seen only in Iniopteryx 
rushlaui). In males a variety of elaborate clasper mech- 
anisms. Tenacular hooks present as in chimaeroids. 
Dorsal fin weak, consisting of a number of fin rays; in 
some specimens of Iniopteryx dorsally fused with one 
another. Tail fin small, circular in lateral view. Ver- 
tebral column consisting of paired, simple neurapophy- 
seal cartilage rods and paired cartilage pieces (arcualia) 
beneath the notochord. Spiral membrane within spiral 
intestine coiled as in sharks with at least 14 turns in- 
stead of three as in modern chimaeroids. 

So far, known exclusively from Pennsylvanian 
black, carbonaceous, sheety shales (and one specimen 
from a Pennsylvanian concretion of otherwise unknown 
locality and horizon) of Westphalian C to Stephanian 
A age of the midcontinent of North America. 

Five genera and seven species are presently recog- 
nized, most of them typical members of the Mecca 
fauna (Zangerl and Richardson, 1963). 

Family Iniopterygidae, nov. 

Characterization. — Iniopterygia in which the denti- 
tion consists of individual teeth arranged in labio-lin- 
gual rows (tooth families) as in sharks (including sym- 
physeal ones), and Meckel's cartilages are not fused at 
the symphysis. 

Genera. — Iniopteryx and Promexyele 

Genus Iniopteryx, 1 gen. nov. 

Characterization. — Most generalized genus of the 
order. Skull without mouth plates. Dentition con- 
sisting of individual, tiny denticles, mostly simple- 
conical, more rarely with minute side cusplets, probably 
arranged in labio-lingual rows (tooth families) as in 
sharks. Symphyseal tooth rows above and below modi- 
fied into tooth whorls with grossly enlarged tooth bases 
not fused to one another. Mucous membrane denticles 
in the region of the branchial arches. Vertebral column 
consisting of about 40 vertebrae, about 20 being pre- 
pelvic. Pectoral fin with large, squarish basal cartilage 
plate, and 11 or more finrays, the anteriormost of which 
is greatly enlarged. Near posterior edge of pectoral fin, 
cartilage rodlets oriented at right angles to the finrays, 
forming an aileron. 

In males anterior fin rays of pectoral fins enlarged, 
each provided with sharp denticles, diminishing in size 
distad. Pelvic fin bases elongated-triangular, each 
bearing a double tenacular hook in the male. Clasper 
apparatus consisting on each side of a proximal rod fol- 
lowed by about a dozen short cartilage pieces that taper 
to a point posteriorly. 

Type species. — Iniopteryx rushlaui, n. sp. 

Iniopteryx rushlaui, 2 n. sp. 

Type.— FMNH PF6678, tf, well-preserved, articu- 
lated, nearly complete skeleton, lacking part of the 

Horizon and locality. — Stark shale, Dennis forma- 
tion, Bronson group, Missouri series, Westphalian D, 
Pennsylvanian. From Limestone quarry, Ft. Calhoun, 
Nebraska. Collected by Mr. W. Rushlau of Omaha, 

Referred specimens. — 
Wea shale 


PF6677, d\ anterior half of skeleton in side view, (W. 

PF6675, d\ anterior half of skeleton, side view, (G.R. 

PF6674, d\ whole skeleton in side view, (W.D. White) 
PF6673, a\ partial skeleton, (W.D. White) 

1 From !?u'on = nape, and pteryx=f\n. 

'■ Named after Mr. William Rushlau of Omaha, Nebraska, who 
has collected the holotype as well as other specimens of inioptery- 


PF6669, — , isolated tail fin, (G.R. Case) 
PF6667, — , isolated pectoral fin base, (G.R. Case) 
PF6666, d\ anterior half of skeleton, (W.D. White) 
PF6676, d\ partial skeleton, (G.R. Case) 


PF6643, d\ articulated partial skeleton, lacking part 

of skull and tail, (W.D. White) 
PF6644, d\ partial skeleton, articulated, (W.D. White) 
PF6683, cf, partial skeleton, (G.R. Case) 
PF6680, cf , partial skeleton, (G.R. Case) 
PF6682, ? 9 , disarticulated pectoral fin, showing prox- 

imally fused finrays, (G.R. Case) 
PF6681, o\ pectoral fin, (G.R. Case) 
PF6752, d\ partial skeleton, (W.D. White) 
PF7128, cf , partial skeleton, (W.D. White) 
PF7123, d\ partial skeleton, (W.D. White) 
PF7126, — , disarticulated skull, (W.D. White) 
PF7125, d\ posterior half of articulated skeleton, (W. 

D. White) 
PF7191, cf , partial skeleton, (G.R. Case) 
PF7167, cf , disarticulated skeleton, (W.D. White) 
PF7190, c? , gastric residue containing this species, (W. 

D. White) 
PF7170, 9 , anterior portion of articulated skeleton, 

(W.D. White) 
PF7188,? 9 , disarticulated skeleton, (W.D. White) 
PF7166, d\ partly articulated skeleton, (W.D. White) 
PF7189, cf , anterior half of articulated skeleton, (W. 

D. White) 
PF7145, d\ skull and shoulder, (W.D. White) 
PF7146, 9 , skull and shoulder, (G.R. Case) 
PF7139, d\ disarticulated skeleton, (W.D. White) 
PF7133, — , jaws and teeth, (W.D. White) 
PF7153, d\ gastric residue, containing remains of this 

species, (G.R. Case) 
PF7222, — , part of skull, (W.D. White) 
PF7211, cf , anterior half of articulated skeleton, (Eric 

Scott Shields) 
PF7220, d", articulated skeleton lacking skull, (W.D. 

PF7219, d\ excellent braincase, definitely associated 
with elements of J. rushlaui, (W. D. White) 

Stark shale 

Ft. Calhoun 

PF6672, d\ articulated skeleton, (G.R. Case) 
PF6761, c? , articulated specimen, lacking pelvic area 

and tail, (W. Rushlau) 
PF6671, — , isolated tail fin, (W.D. White) 
PF6645, d\ excellent skeleton in side view, lacking tail, 

(G. R. Case) 
PF6646, cf , excellent skeleton, nearly complete, (W.D. 

PF6658, d\ disarticulated specimen, (W. Rushlau) 

PF6691, 9 , articulated skeleton, lacking skull and 

much of shoulder, (G.R. Case) 
PF6648, cf , anterior half of articulated skeleton, (G. R. 

PF6765, cf , partial skeleton, (W.D. White) 
PF7192, d\ partial skeleton, (W.D. White) 
PF6703, cf , excellent skeleton in side view, lacking tail, 

(G.R. Case) 
PF6647, cf, anterior half of large specimen, (W.D. 

PF6665, cf, minced skeleton, (W. Rushlau) 
PF6664, — , isolated tail fin, (W. Rushlau) 
PF6754, — , isolated tail fin, (W.D. White) 
U.N.S.M. 1 2906, 9 , anterior half of articulated skeleton 

in dorso-ventral position, (Larry D. Martin) 

La Platte 

PF6649, cf, disarticulated, partial skeleton, (G.R. 


PF6679, cf , gastric residue containing remains of this 

species, (G.R. Case) 
PF7165, cf , partial specimen, (W.D. White) 


PF7176, 9 , juvenile, partial specimen, (W.D. White) 
PF7152, cf , articulated skeleton, (W.D. White) 
PF7132, cf , pectoral fin, (W.D. White) 
PF7181, cf , partial skeleton, (W.D. White) 

PF6662, cf , partial skeleton, (G.R. Case) 

excello shale 

Barret Cemetery 

PF6611, cf, disarticulated remains of pectoral fins 
(XR 2 : Barret 24) 

Logan Quarry Shale 

Logan Quarry 

PF6661, cf , LQS level J, articulated skeleton, lacking 

tail fin (XR: LQ237) 
PF6660, cf , LQS level J, isolated pectoral clasper hooks 

XR: LQ228) 

Hajji Hollow 

PF6587, cf, partly articulated skeleton, incomplete 
(XR: HH5) 

Characterization. — Anterior finrays of pectoral fins 
in males much enlarged and provided with a single file 
of about 13 fishhook-shaped denticles, diminishing in 
size distad. 

Description. — The largest skeletons (i.e., PF6678 or 
PF6645) are between 30 and 35 cm. in overall length. 

U.N.S.M. = University of Nebraska State Museum. 
"XR=X ray plate. 













Fig. 7. Iniopteryx rushlaui, PF6646, region of spiral intestine enlarged to show remains of internal membrane. 

Fig. 8. Interpretation of photograph (fig. 7) of the remains of the spiral intestine of Iniopteryx rushlaui. 



The combined skull and gill arch region of PF6645 
measures about 7 cm. and the visceral portion of the 
body, back to the pelvic area, about 12 cm. 

In a number of specimens (PF6645, PF6646 (fig. 
6), PF6647, PF6761, and others) the abdominal cavity 
is filled with a light brownish, extremely fine-grained 
material that proved to be hydroxyapatite (with some 
calcite) '. The beige mass encloses the vertebral column 
which is preserved inside of it. In PF6672 and PF6646 
this substance contains bits of arthropod exoskeleton, 
conodonts, and plant fragments. In PF6645 and es- 
pecially in PF6646 the hydroxyapatite mass is bounded 
by a gray-bluish surface that shows darker bluish, di- 
agonal stripes, and an extremely fine striated surface 
texture (figs. 7, 8) . These structures are almost beyond 
doubt the casts of the inner surfaces of the spiral intes- 
tine, burst open following bloating, and the beige mass 
is gastric and /or intestinal content that oozed out of 
the digestive tube into the peritoneal cavity during the 
earliest phases of post-mortem bacterial degradation. 


The present understanding of the skull and visceral 
skeleton of this species is very unsatisfactory, in spite 
of the fact that a large number of skulls is at hand. 
The specimens from Nebraska do not produce good ra- 
diographs, a fact that constitutes a major handicap. 
The neurocranium and visceral skeleton are invariably 
collapsed into a near two-dimensional layer of calcined 

1 Dr. Edward Olsen, Curator of Mineralogy at Field Museum 
kindly provided the analysis. The specimen analyzed was PF6645. 

Fig. 9. Braincase of Iniopleryx rushlaui, PF2919, in dorso- 
ventral position. Plate and counterplate. 

cartilage and it is not possible to recognize with con- 
fidence the shapes and complexities of either. 

In PF2919 the braincase is preserved isolated, iu 
dorso- ventral position (fig. 9). However, the plate and 
counterplate do not show the dorsal and ventral sur- 
faces of the neurocranium, rather the break lies near 
the presumed dorsal side. This is suggested by the fact 
that the counterplate shows a pronounced, rounded, 
sagittal ridge fitting into a corresponding groove on the 
plate side. This does not seem to be the proper relief 
for the base of the brain case. The nasal end of the 
neurocranium is narrow, bounded laterally by sharply 
defined, concave outlines that suggest that this denotes 

Fig. 10. Iniopleryx rushlaui, PF6645, anterior portion of skeleton preserved in side view. Arrows point toward enlarged calcined 
cartilage prisms that may have formed the rim of the orbit. 




' / 

y *£T 





Fig. 11. Iniopteryx rushlaui, PF6675. Photograph of a polysulfide rubber cast (Smoothon) of the specimen in lateral position. 

the position of the orbits. Slightly behind mid-length 
the neurocranium suddenly becomes much wider and 
that may be the place of articulation of the palato- 
quadrates with Meckel's cartilages, but well-defined 
articular facets are not developed as in Iniopera (fig. 
61), for example. However, there is no evidence of 
separate palatoquadrates and it may be confidently 
stated that the skull is autostylic. There appear to be 
some striking differences between this braincase and the 

similarly preserved one of Promexyele peyeri (figs. 32, 
33). But we are not yet able to state to what extent 
these apparent differences are due to the mode of preser- 
vation and the plane of splitting. 

The size of the calcified cartilage prisms varies con- 
siderably in different parts of the skull of all inioptery- 
gians, but in Iniopteryx there are rows of extra large 
prisms where one should expect the position of the eyes, 
and we thus assume that the rims of the orbits were 



Fig. 12. Iniopteryx rushlaui, PF6761. Camera lucida drawing of Meckel's cartilages and 
a few teeth to show the size relationship. 





f 7 



. — , / PART OF BASE 

Fig. 13. Camera lucida drawings of jaw teeth of Iniopteryx rushlaui. a, PF6675, anterior end of Meckel's cartilage (Mc.) with the 
symphyseal tooth row above it and a scatter of side teeth; b, (top row) PF6658, a variety of teeth, including a symphyseal one to show 
morphological detail; (bottom row) PF6761, more posterior dentition teeth. 

lined with these especially large calcifications (fig. 10). 
The Meckel's cartilages are rather slender rods, not 
fused at the symphysis (fig. 11). 

The dentition is not preserved perfectly in place in 
any specimen. It is composed of a large number of 
individual, small, morphologically simple denticles, con- 
sisting of conical, slightly recurved crowns and some- 
what expanded bases (fig. 12). Only rarely is a denticle 
seen that has tiny side cusplets (fig. 13). The dentine 
of the crowns looks solid and we presume that it con- 

sists of orthodentine. The pulp cavity is undivided 
and not filled with trabecular dentine (fig. 13). As may 
be seen from Figure 13, the size and the shape of the 
denticles vary considerably. At this time we are un- 
able to differentiate teeth of the upper dentition from 
those of the lower jaw and there is good reason to be- 
lieve that both upper and lower teeth are represented in 
Figure 13, and that differently shaped teeth belong to 
different tooth rows (tooth families) and/or different 
positions within the rows. Along the symphyses of 





1 " >>* 

^ • 

' c 

Fig. 14. Iniopteryx rushlaui, PF6645, photograph of polysulfide rubber cast (Smoothon) of the upper and lower symphyseal tooth rows. 

both Meckel's cartilages and the palatoquadrates (pre- 
sumed fused with the neurocranium) the sagittal tooth 
rows form tooth whorls of somewhat different shapes 
(figs. 13-15). Successive teeth — not fused to one an- 
other — in these whorls are of notably different size 
(fig. 13) indicating the rate of growth of these animals 
between the formation of successive tooth anlagen. 

Well behind the areas where the mouth teeth are 
usually preserved in heaped accumulations and where 
one would expect the presence of pharyngeal gill arches, 
several specimens show additional accumulations of 
denticles. These denticles are usually in linear distri- 
bution which suggests that they were positionally re- 
lated to the arches. The denticles that appear to belong 
to the same arch are of about the same size though there 

is some variation; based on this criterion there seem to 
be three pairs of gill arches that carry denticles, the 
anteriormost bearing the smallest denticles, the most 
posterior one the largest (fig. 16). From the position 
of the largest mucous membrane denticles relative to 
the entire head region it seems safe to say that they be- 
long to the last pair of arches, and that the last three 
pairs bore denticles. But it does not necessarily mean, 
of course, that Iniopteryx had only three pairs of such 


Fig. 15. Semi-diagrammatic illustration of the lower denti- 
tion of Iniopteryx rushlaui, as presently interpreted. 

Fig. 16. Camera lucida drawings of mucous membrane den- 
ticles of ?gill area of Iniopteryx rushlaui. a, PF6645; b, PF6646, 
showing denticles of presumably different gill arches, see text. 

Fig. 17. Iniopteryx rushlaui, PF6661. Drawing made from enlarged stereo radiographs. 



50 mm 

Fig. 18. Iniopteryx rushlaui, PF6678, holotype. Drawing made from enlarged photograph of the plate (fig. 20). 


Fig. 19. Photograph of Iniopteryx rushlaui, PF6678, holotype, counterplate. 

Fig. 20. Photograph of Iniopteryx rushlaui, PF6678, holotype, plate (see also fig. 18). 




Fig. 21. Iniopteryx rushlaui, U.N.S.M. 2906, a female specimen in dorso-ventral position. Note moderate 
enlargement of first pectoral finray and absence of "fishhooks" alongside of it. 

elements. At this time the full complement cannot be 

In PF6646 there are a few fairly large denticles so 
located in the specimen that it seems unlikely that they 
belonged to either the mouth dentition or the last 
pharyngeal arches. They might have been attached to 
the mucous membrane of the palate or to a basibranch- 
ial element. 

In several specimens, but most impressively dis- 
played in PF6677, PF6661, PF7170, and PF7181, there 
are six to ten calcined cartilage rays extending from the 
ventral side of the skull after the fashion of fin rays and 
pointing postero-ventrad (fig. 17). These cartilages 
increase in size backwards and, considering the skull as 
a whole, are relatively large. It cannot be determined 
what relation they have to other elements of the head 

region, but the most reasonable interpretation is that 
they are hyoid radials associated with the opercular flap 
as in chimaeroids. If so, they are relatively larger in 
Iniopteryx and not fused proximately. 

Vertebral column: 

A minimum of 40 segmental units comprise the ver- 
tebral column and about half that number constitute 
the tail peduncle and the tail fin. One can clearly dis- 
tinguish a row of dorsally pointed, elongated cartilage 
pieces that occupy the position of neural arches. Ven- 
tral to them there is often a vacant space (figs. 17, 18), 
presumably denoting the position of the notochord. 
Ventral to this space there is another antero-posterior 
row of paired, small, subrectangular cartilage pieces. 
These are in proper position for ventral arcuals. As in 



modem chimaeroids, there are no vertebral centra. The 
condition differs from that in chimaeroids by the fact 
that successive elements of dorsal and ventral arch 
pieces in the row are of the same size and shape; no dis- 
tinction can be made between basidorsals and interdor- 
sals per segmental unit as in chimaeroids (e.g., Schauins- 
land, 1903; Dean, 1906; Rauther, 1933; and Patterson, 
1965, in the case of the fossil chimaeroid Squaloraja 
polyspondyla) . In Iniopteryx there is, in fact, no evi- 
dence that dual elements per vertebral unit exist; 
rather, it seems that each vertebral element consists of a 
pair of dorsal arch pieces (neural arches) and a pair of 
ventral arcualia. The notochord remained entirely un- 
calcified. In the region of the tail peduncle both the 
dorsal and ventral arcualia are much smaller than in the 
thoracic region of the column and they appear to be 
somewhat incompletely calcified and hence are not dis- 
tinctly outlined (figs. 18-20). Just anterior to the tail 
fin, however, there are again much larger cartilage 
pieces that may or may not be fin rays (fig. 18). The 
vertebral column extends to the very tip of the caudal 
fin where there is a larger, oblong piece of cartilage that 
may represent a fusion of arcualia (fig. 18). 

Shoulder girdle and pectoral fins: 

The shoulder girdle consists of two fairly stout ele- 
ments immediately behind the gill area, curved in such a 
way that the ventral ends extend a little distance for- 
ward beneath the throat region (fig. 17). Near the dor- 
sal ends of these cartilage pieces and on their posterior 
faces there are convex joint facettes for the articulation 
of the basal plates of the pectoral fins. In PF6661, 
drawn from enlarged stereoscopic radiographs, the joint 
processes appear to be located almost at midlength of 
the shoulder girdle pieces but this may not be the cor- 
rect interpretation of the complicated shadow picture. 
It is not certain that the portion above the joint process- 
es is as long as indicated in Figure 17. The element here 
described is best interpreted as a scapulocoracoid such 
as is found in sharks and chimaeroids; the right and left 
halves are not fused in the midline. Attached to the 
scapulocoracoids are two large squarish basal cartilage 
plates that bear the finrays (figs. 17, 18). The shape 
and size of these basal cartilage plates are characteristic 
for the genus Iniopteryx. At their antero- ventral corners 
they bear a shallow notch for the attachment to the 
articular knob on the scapulocoracoids. Diagonally 
across the plate, at the postero-dorsal corner, there is an 
articular knob to which the first (in swimming position 
the anteriormost) , enlarged fin ray is attached. The fin 
is a most remarkable structure embodying features that 
are (to our knowledge) unique among vertebrates. The 
enlarged first fin ray is moderately enlarged in females 
(fig. 21), 1 strongly enlarged in the males where it bears 
a single file of 13 (several, though not all, specimens 

1 At this point it is not possible to distinguish female specimens 
of /. rushlaui from those of /. tedwhitei. Since /. rushlaui is very 
much more common than the other species, it seems probable that 
the specimen illustrated in Figure 21 belongs to /. rushlaui, but 
there is no certainty. 

Fig. 22. Camera lucida drawing of pectoral fin of Iniopteryx 
rushlaui, PF7032, showing an exceptionally complete fin with the 
transversal struts near the posterior edge of the fin (see also fig. 10). 

yield this exact count) fishhook-shaped denticles (figs. 
17, 22). The recurved parts of the "fishhooks" face for- 
ward and the tubular bases (fig. 22) seem to be em- 
bedded, at least partially, in the cartilage of the finrays 
(fig. 17). Each fishhook denticle contains a simple pulp 
cavity, surrounded by a relatively thick coat of ortho- 
dentine. The crowns are glossy, probably covered with 
a thin layer of vitrodentine. Next to the enlarged, first 
finray there are a minimum of ten (PF7032) slender 
ones, decreasing in length and diameter slightly toward 
the last (fig. 22). At the (functionally) posterior side of 
the fin there are also structures that have no homologs 
or analogs in any other fishes: tiny calcified cartilage 
rodlets that extend from two or three posterior finrays 
and at about right angles to them toward the posterior 
margin of the fin (fig. 22) . Some of these rodlets appear 
to be branched and we cannot be certain that they all 
originate from the same finray. Functionally, these 
rodlets perhaps served the same function as the struc- 
tural skeletons within ailerons on airplane wings. 

Pelvic girdle and pelvic fins: 

The pelvic girdle consists of two rather featureless 
pieces of cartilage (figs. 17, 18, 23) that are not likely to 
have been in contact with one another ventrally. At- 
tached to each of these small pelvic elements is a rela- 
tively large, subtriangular plate, the basipterygium that 
bears the finrays of the pelvic fin. The basipterygium 
also consistently bears a large double "fishhook" den- 
ticle (figs. 17, 23) which no doubt served as tenaculum. 
In chimaeroids the tenacular hooks are located on a 
ventro-lateral process of the pelvic element. The pelvic 
finrays, at least nine in number, are short and distally 
followed by ceratotrichia (fig. 24). 

The condition of the pelvis in females (which are ex- 
ceedingly rare in the collection) is not known. The 
clasper apparatus of Iniopteryx rushlaui consists of a 
pair of elongated, proximal cartilage rods followed by 15 
or more consecutive, short cartilage pieces on each side 
that taper to a point posteriorly (figs. 17, 18, 23). Eaeh 
clasper is evidently attached to the antero-medial edge 
of the basipterygium. There are no clasper hooks at the 
distal ends of the clasper structures. 



Fig. 23. Reconstruction of pelvic complex of a rf 1 Iniopteryx 
rushlaui showing pelvic fin with short finrays and ceratotrichia as 
seen in PF7125 (see fig. 24). 

Unpaired fins: 

The dorsal fin is located dorsal to the pelvic region 
(figs. 18, 20). It consists of about six finrays that are 
dorsally fused into a sagittal cartilage plate. There 
may also be fusion of the rays proximally, as for exam- 
ple, in the type specimen PF6678 (fig. 18) . 

The caudal fin is nearly circular in side view (figs. 18, 
25). About 15 functional finrays form the dorsal lobe 
and about an equal number form the ventral lobe. In 
the posterior region of the tail peduncle there are a dor- 
sal and a ventral series of cartilage pieces resembling 
small finrays that seem to grade into the tail fin. Be- 
tween the dorsal and ventral finrays there is a mass of 
cartilage pieces whose shapes are not discernable, and 
the center of the posterior half of the caudal fin is 
formed by an oval cartilage plate (see p. 17). 

The morphological interpretation of this caudal fin 
is obviously difficult since the involvement of the 
arcualia of the vertebral column cannot be made out in 
the present material. A conservative interpretation 
would compare this fin with the caudal of one of the 
Paleozoic sharks in which the dorsal lobe consists of the 
modified arcualia that accompany the notochord, and 
the ventral lobe consists of cartilaginous fin radials. 
With this model in mind one would identify the dorsal 
functional finrays as modified neurapophyses, the in- 
distinct cartilage elements and the terminal, oval plate 
as modified ventral arcualia. The ventral finrays would 
be homologous to the radials in the ventral lobe of the 
shark caudal fin. 

Appearance in life: 

In Figure 26 we have attempted to give an idea of 
what Iniopteryx rushlaui may have looked like in life. 
In overall habitus (though not in any details) Iniopteryx 
resembled Chimaera: head higher than wide and rela- 
tively large; thorax ovoid and fairly sharply set off 
against the tail peduncle; large pectoral fins and rela- 
tively large pelvic fins; tail fin symmetrical; skin naked 
(though in chimaeroids there are dermal denticles along 
the sensory lines). Beyond these rather broad similari- 
ties Iniopteryx rushlaui differed in appearance very 
much from all modern and fossil chimaeroids. The 

most striking feature is the attachment of the pectoral 
fins high up on the shoulder girdle; the morphology of 
the fins strongly suggests that the pectorals were held 
horizontal and at a right angle to the main axis of the 
body (fig. 27). The tail fin probably was no larger than 
the distal ends of the finrays indicate to judge by the 
finray relationship in the tails of sharks like Cladodus or 
Cladoselache. The dorsal fin of Iniopteryx was probably 
supported by the dorsal, fused part of the basal fin ele- 
ments and may have been fleshy or membranous above 
it. In life the rims of the orbits may have been fairly 
prominent and the gill region was covered by mem- 
branous flaps supported by cartilage rods, much as in 
modern chimaeroids. 

Functional matters. — The relative size of the pectoral 
fins and their position high up on the side of the body 
indicate that this pair of fins was the principal locomo- 
tor organ. The articulation of the large basal cartilages 
with the shoulder girdle elements leaves little doubt 
that the fins were moved vertically rather than fore and 
aft, possibly much as in the cheloniid sea turtles: in 
both cases the flipper (or fin) has a sturdy anterior edge 
and a thin, flexible posterior fringe. In the sea turtles 

Fig. 24. Camera lucida drawing of pelvic fin of Iniopteryx 
rushlaui, PF7125, showing ceratotrichia. 



Fig. 25. Enlarged tail fin of Tniopteryx rusMaui, PF6678, counterplate. 

there is a certain amount of axial rotation of the flipper 
during the downstroke and upward recovery ; the same 
was most likely true of the fin of Iniopteryz, to judge 
from the position of the scapular attachment facette of 
the basal fin cartilage at its postero-medial corner (fig. 
26). The large cartilage plate, and especially its ante- 
rior part, very probably served for the insertion of 
powerful muscles both dorsally and ventrally that orig- 
inated on the shoulder girdle and could effect not only a 
downstroke, but also an axial rotation of the fin such 
that its stiff anterior edge was lower than the posterior 
edge during the downstroke, and reversed relations dur- 
ing upward recovery (fig. 28). The tail fin was most 
likely used during slow swimming and propelled the 
animal by the usual lateral motions of most fish tails. 
During faster propulsion, by means of the pectoral fins, 
the tail almost certainly served for steering. The dorsal 
fin and the pelvic fins probably acted as stabilizers. 

Food. — The stomach and /or intestinal contents of 
several specimens contain remains of arthropods, cono- 
dont "denticles," and plant remains. The dentition of 
Iniopteryx rushlaui consists of such delicate denticles 
that the animals probably could not cope with anything 
other than soft-bodied food. 

Sex ratio. — Of 56 specimens in which the sex can be 
determined, only seven are females and two of these are 
doubtful. The reason for this disparity is almost cer- 
tainly predation (see Zangerl and Richardson, 1963). 
It seems probable that the males with their series of for- 
ward looking hooks along the first finrays of the pectoral 

fins could hold the fins at a right angle to the body axis 
thus discouraging all but the largest predators from en- 
gulfing them whole, while the unarmored females could 
be subdued much more easily. 

Geographic, stratigraphic and paleoecological relations. 
— Iniopteryx rushlaui is a member of the Mecca fauna 
(Zangerl and Richardson, 1963; in press) and a beauti- 
fully articulated skeleton (PF6661) comes from the 
Logan Quarry shale in Parke County, Indiana. Most 
of the specimens, however, have been found in strati- 
graphically higher black shales in localities around 
Omaha, Nebraska. These black shales are sandwiched 
between massive limestones and the paleogeographic 
circumstances of their deposition undoubtedly differed 
from those of the Mecca or Logan Quarry shales in 
Indiana. Their origin, as flotant sediments (Zangerl 
and Richardson, 1963), on the other hand, was probably 
the same. 

The Stark and Wea shales in eastern Nebraska, on 
the whole, tend to be limier than the black sheety shales 
that overly coals (e.g., the Mecca and Logan Quarry 
shales in Indiana) and it is at least possible that 
Iniopteryx rushlaui preferred a more carbonate-rich 
habitat. This conclusion is mildly supported by the fact 
that iniopterygians of other genera are barely more 
abundant in these shales and localities than is Iniopteryx 
in Indiana. The presently known stratigraphic range of 
this species is Westphalian C to Westphalian upper D 
(fig. 1). 


/ f I 























Fig. 27. Presumed body outline in ventral view of Iniopieryx rushlaui showing (top) our interpretation of the normal position of top 
pectoral fins during locomotion; (bottom) possible defense or threatening position of the pectoral fins. 

Iniopteryx tedwhitei, 1 n. sp. 

Type.— FMNH PF7241, d\ articulated skeleton 
lacking tail region and clasper mechanism. 

Horizon and Locality. — Wea shale, Westerville for- 
mation, Kansas City group, Westphalian D, Pennsylva- 
nian; Papillion, Nebraska; collected by Mr. W. Rush- 
lau, 1970. 

Referred specimens. — 
Wea shale 

1 Named for Mr. W. D. White of Omaha, Nebraska, the most 
avid collector of iniopterygians. 


PF6709, c? skeleton lacking skull and shoulder-girdle, 
(W.D. White) 

PF6753, d\ part of a skeleton, (W. Rushlau) 

Stark shale 


PF7202, d\ partial skeleton, (W. D. White) 
PF7242, d\ good skeleton, (W. D. White) 



Fig. 28. Assumed swimming positions of the pectoral fins of 
Iniopteryx rushlaui (see text). 


PF5900, cf , part of skeleton showing rasp hooks 

Characterization. — Anterior finrays of pectoral fins 
in males moderately enlarged and covered by several 
rows of denticles with very much enlarged bases and 
straight (not recurved) crowns. Denticles diminish in 
size distad. 

Description. — The rasp denticles of this species are 
so distinctly different from those of all other inioptery- 
gians, and especially from those of Iniopteryx rushlaui, 
that in the absence of other features, one would not con- 
sider this a species of Iniopteryx. The skulls of the type 
specimen and of PF7242 show, however, that the 
dentition consists of simple, individual denticles, exactly 
as in /. rushlaui (fig. 15) and the enlarged symphyseal 
denticles appear also to be the same. Furthermore, the 
type specimen shows the typical, enlarged calcified car- 
tilage prisms, that probably formed the rims of the 
orbits in the genus (fig. 29). 

The rasp denticles — one cannot call them "hooks" — 
consist of slender, straight crowns and very much en- 
larged, saddle-shaped bases (fig. 30). On the fin rasp 
they point backward (as preserved) and may have 
pointed backward and outward in life. In PF7241 the 
skin of the rasp that held the denticles evidently 
sloughed off during degradation and flattened out near 
the body so that the denticles in this specimen form 
patches of pavement. Other specimens show clearly, 
however, that these are not dermal denticles of the body 
skin, but that they are, indeed, attached to the first ray 
of the pectoral fin forming a rasp. 

None of the presently available skeletons of this 
species add to the knowledge of the genus. Iniopteryx 
tedwhitei appears to be far less common than /. rushlaui, 
and there are no specimens of /. tedwhitei from localities 
in the Illinois basin. At the present time female speci- 
mens of this species cannot be distinguished from those 
of /. rushlaui, thus it is not entirely impossible that 
some of the female individuals listed under I. rushlaui 
actually belong to this species. 

Genus Promexyele, 1 gen. nov. 

Characterization. — Generalized iniopterygians. Den- 
tition consisting of individual teeth with two side 
cusplets each that probably stand in labio-lingual rows 
(tooth families) as in sharks; bases of these teeth slightly 
expanded beyond crowns and very rough beneath. En- 
larged symphyseal tooth rows present, but not well 
known. Vertebral column, so far as known, similar to 
Iniopteryx. Pectoral fin very long, with much smaller 
fin base cartilage (basipterygium) than in Iniopteryx; 
six or more finrays with the first (anteriormost) en- 
larged in males and studded with hook-shaped denticles 
that have enlarged bases and decrease in size distad. 
Pelvic basipterygia triangular, little elongated. Mul- 
tiple tenacular hooks (in males) on either side, ap- 
parently attached to separate cartilage pieces. 

Type species. — Promexyele peyeri, n. sp. 

Promexyele peyeri, 2 n. sp. 

Type.— FMNH PF5911, somewhat disarticularted 
<? skeleton, lacking some of the skull. XR: Moore- 
head's Bank No. 1 

Horizon and locality. — Mecca Quarry shale, Liver- 
pool cyclothem (Linton formation), Westphalian C, 
Pennsylvanian. Moorehead's Bank, along Little Ver- 
million River, Vermillion County, Indiana. Collected 
June 1, 1961. 

Referred specimens. — 

Labette black shale 


PF6657, — , partly disarticulated anterior portion of 
skeleton, (G. R. Case) 

excello shale 

Bethel church 

PF6495, — , partial skull, XR: Bethel No. 10 
PF7116, d\ partial skeleton, small individual 
PF6516, — , small, partial skeleton 
PF6522, — , head region of small individual. XR: 

Bethel No. 30 
PF6497, — , partial skeleton, XR: Bethel No. 12 
PF6555, — , partial skeleton, very small individual 

XR: Bethel No. 47 

1 From promeces= elongated, and xyele = rasp. 

2 Named in honor of the late Professor Bernhard Peyer, who 
had a lifelong interest in teeth and dentitions of lower vertebrates. 



Fig. 29. Camera lucida drawing of Iniopteryx tedwhitei, PF7241 (holotype). 

Mecca quarry shale 

Mecca quarry 

PF2815, cf, anterior half of skeleton in fair articulation 
Mecca quarry, level A1.2; XR: MQ 171 

PF2916, 9 , anterior half of skeleton in fair articulation 
Mecca quarry, level A1.2; XR: MQ 59 

PF6724, — , gastric residue mass containing teeth and 
tooth plates of Promexyele. Mecca quarry, level 

CL 153, 9, anterior half of fairly large individual. 
From a lateral extension of the original Mecca 
quarry, dug by Mr. John Carlson. XR: MQ 01 


PF5896, d\ skull and pectoral region in fair articula- 
tion, XR: Jeliff No. 4 

Logan Quarry Shale 

Logan quarry 

PF2358, 9 , excellent anterior half of skeleton. Logan 
quarry, level J; XR: LQ 207. 

PF2510, — , small, disarticulated head region. Logan 
quarry, level J 

PF6636, — , partly articulated head and shoulder re- 
gion. XR: LQ 33 

5 mm 

Fig. 30. Camera lucida drawing of the rasp denticles of 
Iniopteryx tedwhitei, PF5900. 

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metencephalon ^c -, f 

medulla oblongata X 

Fig. 32. Drawings of braincase (a, plate and b, counterplate) of Promexyele peyeri, PF6578, using different directions of illumina- 
tion (see also fig. 33). 

PF2364, 9 , partial skeleton in fair articulation. Logan 
quarry, level J; XR: LQ 168 

Characterization. — First fin rays of pectoral fins very 
much elongated and studded with hook-shaped den- 
ticles with large bases (150 plus, on either side). Three 
tenacular double hooks in males on either side. Clasper 
apparatus consisting on each side of about five short 
cartilage segments, followed by an elongated rod bear- 
ing minute clasper hooks at the end. 

Description. — None of the specimens recognized as 
Promexyele peyeri are sufficiently complete to permit the 
description of the overall habitus and body proportions 
of this species. Compared to Iniopteryx rushlaui the 
pectoral fins are relatively longer (fig. 31) and possibly 
narrower and in males the first rays are much more 
heavily armored with hooks — in fact, these rays might 
be described as rasps. Also clearly different in ap- 
pearance from those of Iniopteryx, are the pelvics of 
Promexyele peyeri: they are relatively shorter, perhaps 
broader, and the copulatory apparatus has a different 

The skull is hardly better known in this animal than 
in Iniopteryx. There are similarities in the fact that 
Meckel's cartilages were free anteriorly and relatively 
weak elements. In PF6578 there is a braincase in 
dorso- ventral position, divided on plate and counter- 
plate in such manner that we see the inner dorsal and 
ventral surfaces of the brain capsule. The relief on 
these two surfaces is, of course, minimal, but present 
and quite interesting. It is also difficult to interpret, 
because comparable views of neurocrania of modern 
chondrichthyans seem to be utterly lacking in the litera- 

ture. The shape of this braincase (fig. 32) shows from 
front to back a relatively narrow rostral section, large 
bulbous expansions in the region of the eyes, pro- 
nounced processes of the fused palatoquadrates for the 
articulation of the Meckel's cartilages, and an occipital 
region that is characterized by two posterior projections 
on either side of the presumed position of the foramen 
magnum. In the gross features mentioned this brain- 
case conforms to a number of other iniopterygian brain- 
cases, though few of them show the bulbous expansions 
in the orbital region. The surface relief of the two 
halves has been emphasized in the drawings (fig. 32). 
As the photographs (fig. 33) clearly show, most of this 
relief consists of fairly undisturbed surfaces of calcified 
cartilage prisms which means that we are looking at the 
dorsal and ventral interior wall surfaces of the brain 
case, but it is by no means easy to decide which is the 
dorsal, which the ventral side. The relief on the plate is 
a trifle more complex than that on the counterplate. It 
consists of a fairly well-defined, sagittal depression ex- 
tending from the position of the presumed foramen 
magnum a short distance forward where it divides into 
the narrower depressions that surround a circular struc- 
ture (fig. 32a) and immediately in front of that a some- 
what larger, approximately circular area. In front of 
the latter there is once more a fairly wide, median de- 
pression which seems to widen noticeably at its forward 
end (fig. 32a). Between the median structures de- 
scribed and the articular facettes on the fused palato- 
quadrates there are other elements of surface relief that 
are probably associated with the auditory capsules. If 
the relief features in the median plane are related to the 
morphology of the brain, as would seem reasonable, one 



Fig. 33. Photographs of braincase (a, plate and b, counterplate) of Promexyele peyeri, PF6578. 

should be able to recognize at least a certain resem- 
blance of these structures to the differentiation of mod- 
ern chondrichthyan brains. A recognizable resemblance 
does indeed exist to the dorsal side of the Rhinochimaera 
pacifica brain as illustrated by Garman (1904, pi. 14, 
fig. 3) . From front to back one would recognize depres- 
sions for the telencephalon (anterior widening of the 
median depression), an elongated diencephalon region, 
(proper in length, but much wider than the diencephalon 
of Rhinochimaera would require), the mesencephalon 
and metencephalon complex followed by the medulla 

The relief on the counterplate consists, near the 
posterior end, of a sagittal, narrow ridge, flanked by 
broad valleys that seem to unite in front of the ridge. 
There are also fairly pronounced, longitudinal lines of 
demarcation medial to the bulbous orbital regions as 
well as a large number of smaller features of the relief, 
that may or may not have morphological significance. 
We are unable to relate this pattern to the ventral as- 
pect of the brain of any chondrichthyan, which renders 
the interpretation of the plate, as reflecting the dorsal 
aspect of the brain, doubtful. 

The dentition consists of a large number of tricusped 
teeth consisting of a main crown cusp and two side 
cusplets which, probably depending upon their position 
in the dentition, are nearly of the same size or differ 
considerably in size (fig. 34). The bases of these teeth 
are slightly expanded beyond the crowns and are char- 
acteristically rough on the underside (fig. 34). We as- 

sume that these teeth stood in labio-lingual rows (tooth 
families) on the jaws in typical shark fashion (fig. 35). 
Several teeth in each row were probably functional at 
the same time. Symphyseal tooth rows are apparently 
present, but in none of the specimens are they preserved 
in situ: in the type specimen (PF5911) there are three 
differently shaped teeth located in a row which might be 
symphyseal teeth. These teeth are single-cusped, ex- 
cept for the middle one which bears one minute side 
cusplet. An idea as to how the dentition may have 
looked is given in Figure 35. 

In contrast to Iniopleryx, the mouth cavity of 
Promexyele was partially covered with denticles that 
fused basally to form a number of tooth-studded plates 
(fig. 34) of different shape and size (not unlike those of 
Sibyrhynchus denisoni, see below) . There is at present 
no specimen that shows these plates sufficiently com- 
plete and in place to permit their designation as ele- 
ments of the floor or the roof of the mouth cavity. 
Tentative identification, however, can be achieved by 
comparison with similar elements in Sibyrhynchus (fig. 
47). PF2358 does show the plates in the area of the 
mouth cavity and an array of cartilage rays that 
probably supported the opercular flap (fig. 36) . 

The shoulder girdle elements are best seen in 
PF2916, PF2358, and CL153. These are long cartilage 
bands curved around the posterior end of the skull and 
reaching a considerable distance forward on the ventral 
side (fig. 36). The articulation with the basal elements 
of the pectoral fins is far dorsal on these elements, pos- 



V Si 




: ' #< 


ay > 

lrell!^^w^ , 

Fig. 34. Promexyele peyeri, PF5911 (holotype). a, scattered 
dentition teeth (arrows) showing the tricuspid character and, b, a 
portion of the pelvic area showing the pelvic cartilages, one of the 
basipterygia, two tenacular cartilages, and a scattering of tenacu- 
lar hooks. 

sibly somewhat higher than in Iniopteryx. The exact 
shape of the basal element of the pectoral fin cannot be 
determined; it is certainly much smaller (shorter) than 
in Iniopteryx. The first (anteriormost) fin ray is barely 
enlarged in PF2358, surely a female. The number of 
finrays in this specimen is six, including the first ray 
(fig. 36). In males such as the type specimen, the first 
ray is much thicker than the other rays and it was evi- 
dently covered with hooks that gave it the appearance 
of a rough rasp. The hooks decrease in size to the distal 
end where they are minute. These rasp hooks differ 
from those in Iniopteryx in that they have much more 
expanded bases (fig. 37) — little platforms that paved 
much (or all) of the cartilage surface of the ray, each 
bearing a recurved denticle. As in Iniopteryx, the rasp 
hooks are modified dermal denticles consisting of a thick 
coat of orthodentine, in the crown region probably cov- 

ered by vitrodentine, and an undivided pulp cavity. In 
CL153 there are enlarged first finrays but not a trace 
of rasp hooks and the specimen was thus identified as a 
female; the generally good state of preservation of the 
available parts of the skeleton makes it unlikely that the 
rasp hooks were lost during bacterial degradation of the 
carcass. Considering the otherwise notable individual 
variation in these animals it is likely that the first 
pectoral finray in some female individuals reached the 
same size as that of males. 

The pelvic apparatus, although disarticulated, is 
best seen in the type specimen (fig. 31) and the recon- 
struction (fig. 38) is one of several possibilities to be 
verified by future articulated remains. As presently 
interpreted, the vaguely boomerang-shaped pieces seem 
to be the pelvic cartilages; the large triangular car- 
tilages are no doubt the basipterygia (to judge by the 
shape of these elements in Iniopteryx). There are two 
additional triangular elements (fig. 31). The smaller ele- 
ment might be one of a pair of cartilaginous bases for 
the three tenacular double hooks. The larger might be 
its mate, asymmetrically developed, or it might be a 
sagittal cartilage plate associated with the dorsal fin; 
the latter appears to us to be more probable. 

The clasper mechanism (fig. 31 and reconstruction, 
fig. 38) consists on each side of a series of five short car- 
tilage pieces that have two parallel straight sides and a 
convex and a concave outline at present. In life these 
elements probably were circular in cross-section which 
is the reason why we have reconstructed them with their 
flat sides in articulation (fig. 38). These short elements 
are followed by a pair of much elongated rods that taper 
to a fairly sharp posterior end. Near their tips there is 
an accumulation of tiny denticles that probably are the 
clasper hooks (fig. 39) . These are faintly curved needle- 
shaped denticles. 

Fig. 35. Present interpretation of the dentition of the lower 
jaws of Promexyele peyeri. 



Fig. 36. Radiograph of a female specimen of Promexyele peyeri, showing both pectoral fins (arising from the nape of the neck) without 
fin rasps; both scapulocoracoids in situ; the hyoid rays supporting the opercular flap and the presence of mouth plates whose detailed shapes, 
however, cannot be made out. Below the pectoral fins, part of the vertebral column is seen. Specimen PF2358. 

Appearance in life. — The reconstruction attempted 
in Figure 38 assumes that the overall habitus of the 
species was similar to that of Iniopteryx. This seems 
justified in the sense that the vertebral column, dorsal 
and tail fins, to the extent that they are preserved, show 
no difference from the compared genus. 

Locomotion. — The structure of the pectoral fins is 
sufficiently different from Iniopteryx to suggest a some- 
what different effect from a basically similar use of the 
fins. It seems probable that Promexyele peyeri like 
Iniopteryx rushlaui propelled itself by vertical motions 
of the pectoral fins. In this case, however, there are no 
broad attachment surfaces for the fin musculature and 
the fin surface is supported mostly by long, thin car- 
tilage rods. These parameters suggest that the fins 

were highly flexible and the vertical motions were rela- 
tively slow and were lacking power in the downstroke. 
Promexyele pzyeri thus was most likely a slow-moving 
fish that may have had a rather restricted home range. 

Sex ratio. — The total number of specimens that can 
be sexed is rather small (8), and, assuming that our 
identification is correct, there are as many females as 
there are males. 

Geographic and stratigraphic distribution. — Prom- 
exyele peyeri is not particularly common in any of the 
localities tested, and by far most of the specimens come 
from the eastern fringes of the Illinois Basin in Indiana. 
In the younger shales (Westphalian upper D) of the 
western part of the Forest City basin, this species ap- 
pears to be as rare as Iniopteryx is in Indiana. 



I 1 


Fig. 37. Photograph of pectoral rasps of Promexyele peyeri, PF5911 (holotype), showing the large numbers of rasp hooks diminishing 
in size distad. 







a> ft 

o ft 
C a) 

o X 

O o 


CO 2 





Fig. 39. Photograph of clasper hooks near distal ends of elasper elements of Promexyele peyeri, PF5911. 

Referred specimens. — 

Promexyele bairdi, 1 n. sp. 

Type. — PF6710, d\ a large part of a skeleton, lack- 
ing the tail region. 

Horizon and locality. — Wea Shale, Westerville for- 
mation, Kansas City group, Westphalian D., Penn- 
sylvanian. Papillion, Nebraska. 

1 Named for Dr. Donald Baird of Princeton University, who 
has a deep interest in Pennsylvanian faunas, and who has con- 
sistently given us the benefit of his background and experience. 

Wea shale 


PF7203, d\ partial skeleton, showing the pectoral rasp 
and much of the clasper mechanism, (W. D. White) 

PF7200, d\ skull and shoulder, good pectoral fin, 
(W. D. White) 


Fig. 40. Camera lucida drawing of Promexyele bairdi, PF6710 (holotype) (see also fig. 43). 





Fig. 41. Camera lucida drawing of the pectoral fin of Prom- 
exyele bairdi, PF7200. Note the abrupt reduction in diameter of 
the rasp and the presence of small and large rasphooks near the 
proximal end of the rasp. 

PF7243, d\ partial, articulated specimen, (W. D.White) 

excello shale 

Barret Cemetery 

PF6455, d\ disarticulated skeleton of juvenile individ- 
ual, XR: Barret No. 11 

Characterization. — First fin rays of pectoral fins en- 
larged, but not as much elongated as in P. peyeri, cov- 
ered with a large number of hook-shaped denticles with 
relatively small bases (probably in excess of 150 per 
rasp). Sharp reduction in diameter of rasp in distal 
third of its length. Two or three tenacular hooks 
(?double) on either side. Clasper apparatus extraor- 
dinarily elongated, consisting of at least four much 

elongated pieces of cartilage on each side, the terminal 
one being extremely slender. No clasper hooks at the 
distal end. 

Description. — The type specimen (fig. 40) shows the 
characteristic features of this fish very well, but adds 
little to the knowledge of the genus. The skull is 
notably disturbed. No teeth or mouth plates are vis- 
ible and the cartilages of the head region look delicate 
— all features that characterize many specimens of 
Promexyele peyeri. The head region shows the cartilage 
supports of the opercular flap and some elements that 
probably belong to the hyobranchial apparatus (fig. 40). 

Shoulder girdle and pectoral fins are much disturbed 
except for the pectoral rasps, which show a peculiarity 
not seen in any other iniopterygians, namely, a sudden 
reduction in the diameter of the cartilage rods in the 
distal third of the rasps (fig. 40). Since this feature is 
also present in the referred specimen PF7200 (fig. 41), 
we assume that it characterizes the species. The rasps 
are covered with a large number of hooks (probably 
more than 150 per rasp) all of which are relatively small, 
even at the proximal ends of the rasps. These denticles 
have relatively small bases and thus differ notably in 
shape from those of P. peyeri. Since there are denticles 
of different sizes both in the proximal areas of the rasps 
as well as in the distal parts, it is possible that there are 
specially differentiated rows of slightly larger denticles, 
for example, along the anterior edges of the rasps. In 
addition to the rasp, there are 12 slender rays in the 
pectoral fin of PF7200, seven of which are short and 
stand at an angle to the long ones, thus perhaps forming 
the supports for an aileron, as in Iniopteryx rushlaui. 

The pelvic area is remarkable. The region is slightly 
disturbed in the type specimen so that the exact extent 
of the pelvic elements and the basipterygia (fig. 40) can- 
not be determined with accuracy. If our interpretation 
of the pelvic complex is correct (fig. 42), it would suggest 
that the pelvic cartilages are relatively much larger than 

Fig. 42. Reconstruction of the pelvic complex of the male of Promexyele bairdi, based on several specimens; see also fig. 43. 

Fig. 43. Photograph of Promexyele bairdi, PF6710 (holotype). 




in other iniopterygians, while the basipterygia are rela- 
tively smaller. The uncertainty is due to the fact that 
these elements appear to overlap to an undeterminable 
amount. Off to one side of this complex is a much 
smaller piece of cartilage (or, more likely, two, that par- 
tially overlap) bearing at least five tenacular hooks that 
may or may not be double hooks. Another such hook is 
located at the presumed junction of one of the pelvic 
and basipterygial elements (fig. 40). 

The claspers are extremely elongated and end in a 
thin whip (figs. 42, 43). It is difficult to determine how 
many pieces of cartilage contribute to each clasper, but 
we believe them to be at least four. Apparently there 
are no clasper hooks at the end of the whip. 

Family Sibyrhynchidae, nov. 

Characterization. — Iniopterygia in which the labio- 
lingual tooth rows (tooth families) are basally fused to 
form tooth whorls of different size and shape. Meckel's 
cartilages are fused at the symphysis. 

Genera. — Sibyrhynchus, Iniopera, Inioxyele. 

Genus Sibyrhynchus, 1 gen. nov. 

Characterization. — Iniopterygians with sharp- 
toothed dentition consisting of 12 pairs of different 
tooth whorls; "canine" whorl fifth from symphysis in 
the upper jaw, third from symphyseal whorl in lower 
jaw. Snout armored with three tubercles, a blunt me- 
dian one flanked by two stout tubercles; a large, sharp- 
pointed tubercle projects from the anterior end of the 
lower jaw. Denticulate roof and floor plates of the 
mouth cavity irregular in outline; the denticles tending 
to fuse basally in linear rods that form stellate com- 
plexes, (ca. 5 on either side of the palate). Multiple 
tenacular hooks located on basipterygium. Claspers 
consisting each of a stout proximal cartilage rod, fol- 
lowed by a series (ca. 6) of short pieces and terminating 
in an elongated, distally blunt rod. 

Type species. — Sibyrhynchus denisoni, n. sp. 

Sibyrhynchus denisoni 2 , n. sp. 

Type.— FMNH PF6408, slightly disturbed d" skele- 
ton, lacking the tail. XR: Bethel No. 56. 

Horizon and locality. — Black, sheety shale over coal 
IV-A (Excello shale equivalent), Petersburg formation, 
Westphalian D, Pennsylvanian; stripmine headwall, 
about center of NW y± Sec. 3, T3S, R7W (Augusta 
Quadrangle), about % mile SE of Bethel Church, Pike 
County, Indiana. 

Referred specimens. — 
queen hill shale 

PF7216, — , scatter of hardparts, (M. Eisele) 
PF7224, — , scatter of hardparts, (G. R. Case) 

1 From sibyne= hunting spear, and rhynchos= snout. 

2 Named for a friend and colleague, Dr. Robert Denison, for- 
mer Curator of Fossil Fishes, Field Museum of Natural History. 

Excello shale 

Bethel Church 

PF6504, — , chewed skull, XR: Bethel No. 21 
PF6506, cf , clasper apparatus and partial tail fin. XR: 

Bethel No. 20 
PF6514, — , chewed skull. XR: Bethel No. 26 
PF6515, — , gastric residue including tubercles and 

tooth whorls of Sibyrhynchus. XR: Bethel No. 29 
PF6525, — , gastric residue of very small individual. 

XR: Bethel No. 32 
PF6559, — , gastric residue, containing two specimens 

of different size. XR: Bethel No. 43 
PF6576, — , mutiliated skull 
PF6615, cf, large portion of articulated skeleton with 

good vertebral column and pelvic area. XR: 

Bethel No. 53 
PF6616, — , chewed remains of skull. XR: Bethel No. 

PP6617, — , gastric residue, containing identifiable 

hard structures of Sibyrhynchus. XR: Bethel No. 


Barret Cemetery 

PF6565, — , gastric residue mass, containing hard parts 
of this species. XR: Barret No. 17 

Beaver Pond 

PF6463, — , gastric residue mass, containing hard parts 
of this species. XR: Beaver No. 1 

PF6582, — , gastric residue mass, containing hard parts 
of this species. XR: Beaver No. 3 

Pit 12 

PF6729, — , gastric residue mass containing hard parts 
of this species. XR: C.P.L. No. 13 

Pit 14 

PF6537, — , gastric residue pellet, containing hard parts 
of this species. XR: Pit 14, No. 8 

PF6538, — , gastric residue mass, containing hard parts 
of this species. XR: Pit 14, No. 9 

PF6539, — , partial skull. XR: Pit 14, No. 7 

Mecca Quarry Shale 

Mecca Quarry 

PF2806, 9 , partial skeleton, partly articulated. Mecca 

quarry level B4.1; XR: MQ No. 12 
PF2819, — , mutilated skull of fairly large individual. 

Mecca quarry, level B1.2; XR: MQ No. 226 
PF2835, — , gastric residue spatter of hard parts of this 

species. Mecca quarry, level B3.3; XR: MQ No. 

PF2900, — , scatter of hard parts of this species. Mecca 

quarry, level Bl.l; XR: MQ No. 76 



PF2915, — , gastric residue pellet containing hard parts 

of this species. Mecca quarry, level Al.l; XR: 

MQ No. 167 
PF2918, — , gastric residue with hard parts of this spe- 
cies. Mecca quarry, level B4.2; XR: MQ No. 119 
PF2920, cf . mutilated, partial skeleton. Mecca quarry 

level B4.2; XR: MQ No. 66 
PF2936, — , gastric residue mass, containing hard parts 

of this species. Mecca quarry, level Bl.l; XR: 

MQ Nos. 217, 91 
PF3013, — , gastric residue spatter containing hard 

parts of this species. Mecca quarry, level B1.4; 

XR:MQNo. 228 
PF6716, — , gastric residue mass containing hard parts 

of this species. Mecca quarry, level B2.4 
PF6747, — , gastric residue, containing hard parts of 

this species. Mecca quarry, level Bl.l; XR: MQ 

No. 211 
PF6760, — , gastric residue mass containing hard parts 

of this species. Mecca quarry, level B3.2 
PF6764, — , gastric residue pellet. Mecca quarry, level 

B1.4; XR: MQ No. 212 
PF2940, — , scattered skeleton, Mecca quarry, level 

Bl.l;XR:MQNo. 217, 91 

U.S. Highway 41 

PF1019, — , scattered remains. XR: DS No. 16 
PF1034, — , scattered remains, excellent detail 

PF1036, d\ small articulated skeleton with skull miss- 

Mine Creek 
PF6762, — , isolated hard parts 

Montgomery Creek 

PF6623, — , gastric residue mass, containing hard parts 
of this species. XR: Montgomery No. 2 

West Montezuma 

PF6634, d\ good partial skeleton. XR: Montezuma 
No. 4 

PF6635, — , slightly mutilated skull. XR : Montezuma 
No. 9 

PF6637, c? , gastric residue containing hard parts of this 

PF6639, d\ part of a fair-sized specimen without skull. 

XR: Montezuma No. 18 
PF6641, — , disarticulated, large specimen 

Moorehead's Bank 

PF6650, — , part of a skull with anterior tooth whorls of 
lower jaw and tubercle in place. Collected and 
donated by Mr. John Carlson 

Chinook Mine 

PF5879, — , gastric residue mass containing hard parts 
of this species. XR: Chinook No. 3 

Logan Quarry Shale 

Logan Quarry 

PF2351, d\ gastric residue pellet. Logan quarry, level 

G;XR:LQNo. 301A 
PF2354, — , part of a skull, incompletely recovered. 

Logan quarry, level G; XR: LQ No. 237 
PF2355, — , mutilated skull and shoulder region. Logan 

quarry, level G; XR: LQ No. 194 
PF2363, — , mutilated skull. Logan quarry, level J; 

XR: MQ No. 137 
PF2365, — , gastric residue pellet, containing hard parts 

of this species. Logan quarry, level J; XR: LQ 

No. 37 
PF2592, — , gastric residue, containing hard parts of 

this species. Logan quarry, level G; XR: LQ No. 

PF2594, — , part of a skull with excellent dentition. 

Logan quarry, level G; XR: LQ No. 303 
PF2632, cf, disarticulated, but excellent specimen; 

good braincase, lower jaw. Logan quarry, level J; 

XR:LQNo. 263 
PF6730, — , gastric residue mass containing hardparts 

of this species. Logan quarry, level F 
PF6757, — , scatter of Sibyrhynchus parts. Logan 

quarry, level J; XR: LQ No. 124 

Hajji Hollow 

PF5894, — , mutilated skull. XR: Hajji Hollow No. 3 

Characterization. — Same as for genus. 

Description. — Sibyrhynchus denisoni is probably the 
largest of the presently known iniopterygians, but none 
of the specimens on hand permit a length measurement 
of the entire fish. This species is also easily identified, 
even in gastric residues, because of the relatively large 
size of the tooth whorls, the snout tubercles, especially 
the median upper one which has a characteristic ap- 
perance, the large tubercle on the lower jaw, and the 
spidery tooth plates in the roof and on the floor of the 
mouth cavity. The latter, however, may be confused 
with similar plates in Promexyele. The reconstruction 
(fig. 56) is based on several specimens (mostly PF6408. 
PF6506, PF6615) that are not the same size, hence we 
cannot be absolutely certain that the proportions of the 
various parts of the skeleton are correct, though the 
size factor was taken into account. There are other un- 
certainties : in none of the presently available specimens 
is there definite evidence of a dorsal fin, and the precise 
morphology of the pectoral fin is not determinable at 
this time. 


An excellent neurocranium and disarticulated lower 
jaw are preserved in PF2632 (fig. 44) and a somewhat 
less perfectly preserved skull belongs to PF6634. In 
both cases the neurocranium is seen in dorso-ventral 
position on radiographs. Figure 44 was rendered from a 
pair of much enlarged stereo X-ray pictures according 



Fig. 44. Sibyrhynchus denisoni, PF2632, skull complex drawn from enlarged stereo radiographs. The neurocranium is preserved in 
dorso-ventral position and is seen from the ventral side. 

to[the technique described earlier (Zangerl. 1966). The 
neurocranium, seen from the ventral side in Figure 44, 
shows very clearly the articular facettes for the lower 
jaw; they are part of a ventro-lateral cartilage mass that 
is attached, at the postero-lateral corners of the neuro- 
cranium, to a dorsal cartilage mass. A ventral plate of 
cartilage, furthermore, extends from the articular fac- 
ettes forward toward the blunt snout. Below the fac- 
ettes the ventral cartilage mass shows a transversal 
ridge on either side of a median plate which extends to 
the occiput. The posterior margin of the dorsal car- 
tilage mass shows three pairs of symmetrical projec- 
tions. On the X-ray picture there is no evidence of an 
otic capsule or inner ear structures, the orbits, the nasal 
capsules or the outline of the brain enclosure. 

The reason for this lack of detail, while the overall 
structure is readily recognizable as a neurocranium, is 
the mode of preservation of the three dimensional organ, 
whose external and internal surfaces were supported 

only by single layers of calcified cartilage prisms held 
together by connective tissue. Following death the 
head decomposed by bacterial action in an absolutely 
quiet, completely undisturbed burial environment. In 
the course of this process the cranium settled gradually 
into an essentially two dimensional state with every 
part of the originally vaulted structure being projected 
vertically into the fossil plane. This had, of course, the 
consequence that all curved surfaces and those not 
parallel to the fossil plane, became reduced in area, 
which resulted in wrinkling of the surfaces and more 
often in the local jumbling of calcified cartilage prisms. 
One feature of the skull however, is unmistakable: 
the fact that the palatoquadrates are fused to the neuro- 
cranium in such manner that it is completely impossible 
to surmise the original boundaries of these elements. 
The jaw suspension is thus autostylic, as in chimaeroids. 
The lower jaw consists of symphyseally fused Meckel's- 
cartilages; the rami stand at an angle of about 35-40° in 



PF2632, PF6634, PF6757. This means that the articu- 
lar facettes are closer together in the lower jaw than in 
the neurocranium of PF2632 and we have assumed that 
during decomposition of the neurocranium the articular 
facettes underwent a slight lateral displacement. In 
Figure 45b, the dotted lines indicate the preserved con- 
dition, the solid line our correction to fit the posterior 
width of the mandible. 

Hyobranchial apparatus 

The hyobranchial apparatus of Sibyrhynchus con- 
sists, as far as one can presently determine, of a char- 
acteristic, six-sided cartilage plate whose anterior and 
posterior sides are joint facettes and the element shows 
consistently symmetrically placed foramina (fig. 46). 
In addition, there is a smaller piece, (also provided with 
articular facettes and either a deep central pit or a large 
foramen), a pair of elongated elements with joint 
facettes on one end, and a blade-like flare on the other 
(fig. 46); matching almost perfectly the ceratohyals 
(ceratohyals plus possibly hypohyals, Nelson, 1969) 
figured for Callorhynchus smythi by Garman (1904, pi. 
13-3) . The element with the paired foramina is perhaps 
the first basibranchial and in front of it there was prob- 

ably a glossohyal, not yet seen in this species, but com- 
monly noted in Iniopera (see below), and almost cer- 
tainly present in Sibyrhynchus in light of the anterior 
articular facettes of the first basibranchial. 

In Sibyrhynchus denisoni the snout is armored with 
three strong tubercles consisting mostly of trabecular 
dentine. The medial, blunt one, is highly characteristic 
on radiographs (figs. 44, 47) where both the dorsal and 
ventral sides of the tubercle are visible. The ventral 
edge is nearly straight, while from the dorsal face pro- 
ject a number of long radii far beyond the ventral edge 
(fig. 45a, b). This element is flanked by two more or 
less perfectly conical tubercles, also provided with radii 
on their dorsal sides and straight edges ventrally (fig. 
45a, b). The tip of the lower jaw is provided with a 
much larger, sharply pointed tubercle whose dorsal rim 
is straight, while its ventral side projects into several 
very long radii over the ventral side of the mandible, 
(figs. 44, 45c, d, 47). In Figure 45 we have, further- 
more, attempted to show the dentition of both upper 
and lower jaws, the elongated structures representing 
tooth whorls, and the spidery dental plates of the roof 
and floor of the mouth cavity. 

Fig. 45. Sibyrhynchus denisoni neurocranium and lower jaw with snout tubercles, tooth whorls, and mouth plates. Dotted line is out- 
line of neurocranium as preserved (PF2632, fig. 44); solid line is width of neurocranium adjusted to width of mandible, a, snout tubercles 
from dorsal view; b, snout tubercles, dentition, and palatal plates seen from ventral view (tooth whorls schematized); c, tubercle on lower 
jaw from ventral view; d, tubercle, dentition, and floor plates of the mouth cavity as seen from dorsal view. 




The dentition of Sibyrhynchus (and the genera 
Iniopera and Inioxyele, see below) is most remarkable, 


\ » 

Fig. 46. Hyobranchial elements of Sibyrhynchus denisoni 
with the possible mode of superposition of the denticulated plates 
on the floor of the mouth cavity. Scale: x 0.75. 

indeed. In Sibyrhynchus it consists of six pairs of tooth 
whorls in the upper jaw, and six pairs of whorls plus an 
unpaired symphyseal one in the lower (figs. 45b, d). 
Each pair of tooth whorls differs from all others in the 
shape of the whole structure, and the size and number of 
teeth. Thus Sibyrhynchus displays a degree of dental 
diversity not realized in any other fishes, and rivals or 
even exceeds the heterodonty of the mammalian denti- 

Each tooth whorl consists of a number of teeth, be- 
longing to a labiolingual row, called "tooth family" in 
sharks, whose bases have fused so that the entire tooth 
family has become a tooth whorl in which the individual 
tooth crowns are separated from one another and clearly 
distinguishable from the base (fig. 48a). The enlarged 
base of each whorl consists of lateral sheets of dentine 
that enclose one large space into which open the pulp 
cavities of the component teeth (fig. 48b). In life this 
space was not a cavity. Instead, it was filled with cal- 
cified cartilage, a pronounced ridge on the neurocranium 
or the mandible that formed the seat of the tooth whorl 
(fig. 48b). 

In sharks the state of development of the teeth of a 
tooth family decreases from the functional tooth on the 
edge of the jaw to the anlagen stages at the lingual end 
of the dental lamina (see, for example, Peyer, 1968, pis. 
7a, 8b, 9b). In the early stages of hard substance 
deposition, the teeth contain very large pulp cavities 
enclosed by thin walls of orthodentine covered by vitro- 
dentine; in the fully mature teeth the pulp cavities are 
reduced in volume and the tooth walls have correspond- 
ingly increased in thickness. Precisely the same mode 
of tooth differentiation is seen in an iniopterygian tooth 
whorl; at the lingual end of the whorl the teeth are thin- 
walled and enclose large pulp cavities, a clear indication 
that this end was near the end of the dental lamina. 

One can safely assume that in life younger tooth stages 
preceeded the most immature teeth on the fossil whorls 
and that these were not preservable. Reflecting the 
growth of the animal as a whole the teeth show a dis- 
tinct size increase toward the immature end of the whorl 
(fig. 48a). In contrast to the condition in sharks, how- 
ever, there is no evidence in the tooth whorls that the 
earliest teeth were shed after a certain period of func- 
tion. On the contrary, many whorls show teeth only on 
the middle and posterior (lingual) parts, the anterior 
(labial and oldest) regions being devoid of them. It 
seems probable that the small teeth there have worn off 
during the life time of the individual. 

In none of the specimens is the entire dentition per- 
fectly in place; in fact, instances where numbers of tooth 
whorls are seen in place are rare exceptions. In most 
specimens the whorls are more or less out of place and 
elements of the upper and lower dentitions tend to be 
mixed together, or only a part of the dentition is present 
or visible. Because of these considerable difficulties it is 
not yet possible to describe in detail the morphology of 

Fig. 47. Drawing of snout tubercles, tooth whorls, and tu- 
berculated plates of the mouth cavity of Sibyrhynchus denisoni, 
PF6408 (holotype), made from enlarged stereo radiographs and 
what can be seen on the specimen, a, median tubercle on lower jaw; 
b, median tubercle on snout; c and c', lateral tubercles on snout; 
d and d', additional tubercles about the head; e and e', denticu- 
lated plates on the floor of the mouth cavity; f, denticulated plates 
on the roof of the mouth cavity; g and h, "canine" tooth whorls; 
i, i' and i\ lateral tooth whorls of upper and/or lower jaw. 










Fig. 48. a, Diagrammatic section across the jaw of a shark showing the teeth and tooth anlagen along the 
dental lamina, with the youngest anlagen at the lingual end of the lamina. Below, a section through a tooth 
whorl of an iniopterygian such as Sibyrhynchus, showing the basic similarity to the shark condition; the teeth 
are fused at their bases, but the ones at the lingual end of the whorl are clearly younger teeth than those at the 
labial end. b, Section through an iniopterygian tooth whorl at a right angle to that shown in a. It shows that 
whorl riding on a ridge of cartilage with calcified prisms just beneath the perichondrial membrane (not pre- 
served in the fossils). The tooth crown consists of orthodentine surrounding a pulp cavity that diminishes in 
volume with the age of the tooth crown. 

all classes of tooth whorls, and such identifications as 
we have made are tentative. 

The description of the tooth whorls requires a ter- 
minology, and we shall label them from the symphysis 
outward and backward in series P-l (for palatoquad- 
rate-1) to P-6 in the upper jaw, M-l to M-6 in the man- 
dible which also has an M-s, a symphyseal whorl. 

Upper and lower tooth whorls apparently differ from 
one another in the degree of curvature: the lower ones, 
especially those along the cheek, being flatter than the 
upper whorls. In each jaw there is a pair of whorls with 
large teeth. In the upper jaw it is the fifth from the 
symphysis, apparently in cheek position much as a 
carnassial tooth in a mammal; in the mandible it is the 
third pair, clearly in "canine" position (fig. 45). 

In PF6650 part of the dentition of the lower jaw is 
seen in situ (fig. 49) . The symphyseal whorl bears five 
teeth, the anteriormost two being broken off. The 
crowns are devoid of side cusplets. M-l has seven teeth 
on the left element, which is better exposed. In M-2 
there are eight teeth. In both M-l and M-2 the tooth 
crowns have small side cusplets. The large M-3 whorls 
are incompletely exposed in this specimen, but their 
shape may be seen in PF2594 (fig. 50) where the best- 
exposed element shows four teeth and enough base in 
front and in back to have borne at least three additional 
teeth in life. Next to the right M-3 whorl in PF6650 
there is an elongated element with a row of six teeth 
located on the posterior part of the whorl; a few addi- 

tional teeth may have been in front of the tooth row, 
but the specimen does not permit a definite count. This 
whorl is probably M-4. Behind this whorl there is a 
long gap in the specimen, followed by a very much 
elongated whorl, probably M-6. This bears at least 
eight teeth and is toothless anteriorly (fig. 49). It is 
difficult to identify lower jaw whorls in PF2594 (fig. 50), 
other than the pair of M-3 that lie near the large 
tubercle, save for the fact that mandibular whorls are 
less curved than the upper ones. Thus we tentatively 
identified the two elements behind the large tubercle as 
M-4 and M-5 and the whorl with the nearly straight 
tooth row located between the two lateral snout tuber- 
cles as M-6. Of the upper dentition, pairs of P-l, P-2, 
and P-3 are in place, preserved perpendicular to the 
bedding of the shale and all tooth crowns have been 
broken off (fig. 50). This tooth complex is flanked by a 
paii' of whorls the left one of which is seen in side view. 
These elements are spaced somewhat from the in situ 
complex and we have tentatively identified them as P-4. 
assuming that the small diastema permitted the recep- 
tion of the lower "canine" whorl (M-3). Both P-4 
whorls show a feature not seen in other whorls, namely 
the fact that the anterior teeth are not located on the 
ridge of the whorl, but trend over to its medial side 
(fig. 50) . The significance of this eludes us. Next to the 
left P-4 there is the very much larger P-5 which bears 
six teeth, the last one nearly twice the size of the first. 
The whorl immediately in front of it has been identified 



as P-6 since it is rather strongly curved. It has six teeth 
and a large anterior area devoid of teeth. 

In PF6617 a small whorl, perhaps one of the upper 
front tooth whorls, shows on the sides of each large 
tooth crown a much smaller side cusp and beneath it yet 
another, tiny cusplet (fig. 51). 

In Sibyrhynchus denisoni (and apparently only in 
this genus) there are additional dental structures that 
are especially unusual in a chondrichthyan. These have 
been noted in the general area of the skull in the follow- 
ing specimens: PF2806, PF2918, PF6559, PF6582, and 
PF6617. The peculiar elements are teeth consisting of a 
shiny crown of low relief and a root (dull surface) of un- 
mistakably mammalian character (fig. 52). Inside 
there is a pulp cavity and a typical root canal. 

A thin section through one of these elements in 
PF2918 (fig. 52) shows three tissues: dentine, vitroden- 
tine, and bone arranged exactly as are dentine, enamel, 
and cementum in a mammalian tooth. The dentine, 
however, is chondrichthyan orthodentine with rela- 
tively few dentinal tubules of different caliber, distally 
dividing, and provided with lateral branchlets of min- 
ute diameter. On the crown surface there is a layer of 
vitrodentine with fewer dentinal tubules, and covering 
the entire root there is a layer of bone (fig. 52) whose 
morphology is the same as the bone described in the 
edestid shark Ornitkoprion hertwigi (Zangerl, 1966). 
The bone cells, for the most part, apparently retreated 
as they produced the bone matrix, but a few did be- 
come enclosed within the bone substance. Their ca- 
naliculi extend in an irregular fashion from the cell 
bodies (fig. 52). 

The shape of these teeth varies mostly as regards the 
length of the roots and the symmetry of the entire 
denticle; some are symmetrical, others strongly asym- 
metrical (fig. 52). The number of these denticles per 
specimen seems to be small. 

We do not know where in or on the body these 
strange denticles were located. They are consistently 
associated with skull material and usually not inter- 
mingled with the tooth whorls. It is thus possible that 
they were located on pharyngeal arches. 

Both roof and floor of the mouth cavity of Sibyrhyn- 
chus are lined with mucous membrane denticles that 
have basally fused to form a considerable variety of 
plates that have a vaguely spidery appearance. This is 
due to the fact that the denticles fuse along lines and the 
lines tend to radiate from centers (fig. 47) . In the type 
specimen PF6408 plate and counterplate parted in such 
a way that one set of plates is located on the plate, while 
another set is located on the counterplate, the den- 
ticulated surfaces facing one another. This provided 
the clue that these plates, indeed, lined the mouth 
cavity, not the outside of the head, and made possible 
the decision as to which set of plates covered the roof, 
which, the floor of the mouth cavity. 

On the roof of the mouth there are a pair of larger 
plates, sharply asymmetrical, surrounded by a swarm of 

Fig. 49. Camera lucida drawing of a latex cast of the lower 
jaw of Sibyrhynchus denisoni, PF6650, which shows the anterior 
tooth whorls in position and perhaps also two of the lateral tooth 



Fig. 50. Camera lucida drawing of tooth whorls and snout tubercles of Sibyrhynchus denisoni, PF2594. 
the upper jaw are in place, though the tooth crowns are all broken off. 

Tooth whorls of 

smaller "spiders." In all probability they filled the 
space between the tooth whorls (fig. 45) . On the floor of 
the mouth there is an anterior element of highly char- 
acteristic shape. It consists of an anterior, fairly thick, 
smooth portion followed by a fan of radiating denticle 
lines (fig. 47). This element is followed by at least 
three, fairly large, "spidery" plates. The skeletal sup- 
ports of these floor plates of the mouth cavity lie be- 
tween the rami of the mandible, hence are parts of the 
hyobranchial apparatus. A sketch showing the possible 
relations is shown in Figure 46. 

Vertebral column: 

The vertebral column is partially articulated in 
PF6615 (fig. 53), at least in the region of the caudal 
peduncle. The neural arch pieces appear to be much as 

in Iniopteryx, but the ventral arcuals differ consider- 
ably from those of the compared genus in that there are 
curious ?fused pieces in the region back of the pelvic 
girdle (fig. 53) and in the tail peduncle the ventral 
arcuals have the shape of haemapophyses. We do not 
know whether the seemingly fused arcuals mentioned 
above represent an abnormal, or even pathological con- 
dition, or whether they are a part of the normal 
morphological differentiation of the vertebral column in 
this animal. 

None of the specimens shows evidence of an un- 
paired dorsal fin. The tail fin is partly preserved in 
PF6506. Its structure is very similar to that in Iniop- 
teryx, but it appears to be relatively sturdier and larger 
in Sibyrhynchus (fig. 54). 



I mm 



Fig. 51. Camera lucida drawing of small, probably anterior 
tooth whorl of Sibyrhyitehus denisoni, PF6617, showing lateral 
cusp lets. 

Shoulder girdle and pectoral fins: 

Several specimens show parts of the pectoral fins, 
but in all of them the finrays are broken into small 
pieces so that only the principle can be determined. 
The shoulder girdle cartilage is strongly curved and ex- 
tends ventrally forward beneath the skull. It is much 
more massive in its dorsal half where the basal fin car- 
tilage articulates (figs. 53, 55). The latter is well pre- 
served in PF2632 (fig. 55). This cartilage is an approxi- 
mately rectangular piece provided near one end with a 
strong articular head and opposite this is a deep articu- 
lar pit. The fin has at least three rays of nearly equal 
diameter. The first, even in males, is not much larger 
than the others, but it does bear hooks on little bases as 
in Promexyele peyeri; the number of hooks is much 
smaller than in this genus. There are approximately 40 
hooks on each side in addition to perhaps an equal num- 
ber of very tiny hooks on the distal parts of the fin ray 
that cannot be counted adequately. 

Pelvic area : 

The pelvic area is well represented in a number of 
male individuals (PF6408. PF6506, PF6615, and 
PF6639). The pel vies are vaguely boomerang-shaped 
cartilages to which the basipterygia of the pelvic fins 
are attached. The latter are triangular, but in no case 
sharply outlined and hence perhaps were poorly calcified 
in life. The clasper mechanisms, on the other hand, are 
well preserved. Each clasper consists of a proximal 
piece of cartilage of moderate length followed by a 
series of six pieces (the first being half as long as the 
proximal one) and a distal elongated rod that appears 
to terminate bluntly in all specimens. No terminal 
clasper hooks were noted in this species (fig. 56). There 
are five or six much enlarged tenacular hooks located on 
each side of the basipterygium. 

Appearance in life. — The reconstruction (fig. 56) 
provides only an approximate notion of the appear- 
ance of this fish. Since the drawing is a composite of 
several individuals we are not sure that the proportions 
of the various parts to the whole are entirely correct. 

An interesting matter concerns the slanted position of 
the mouth cleft (fig. 56). If one articulates (on paper) 
the lower jaw of PF2632 with the neurocranium, the 
lower jaw protrudes a considerable distance beyond the 
front end of the snout (fig. 57). This relationship is also 
seen in at least 10 cases where neurocrania are associ- 
ated with the lower jaws in Iniopera (see below). Such 
a relationship would oppose the front tooth whorls of 
the upper jaw to the denticulated plates on the copulae 
of the hyobranchial apparatus, which is hardly credible. 
All the braincases are in dorso-ventral position, and in 
all cases the lower jaws are disarticulated and lie nearby. 
Since the lower jaws became disarticulated very soon 
after death and settled parallel to the burial ground, 
they did not suffer any length distortion. The neuro- 
crania, on the other hand, are complex, three-dimen- 
sional structures. During bacterial degradation in 
absolutely quiet burial microenvironments these struc- 
tures collapsed in such a way that all parts were pro- 
jected vertically onto the burial plane; hence all 




Fig. 52. ?Pharyngeal teeth of Sibyrhynchus denisoni, PF6617, 
that show very flat crowns and long roots. Thin-section, PF2918 
(slide no. 5422), shows a longitudinal section through one of these 
teeth and histological details of the vitrodentine covering the 
crown and the bone covering the root. 

40 mm 

Fig. 53. Radiograph of Sibyrhynchus denisoni, PF6615. The neurocranium is enveloped in a thick mass of pyrite. In upper right cor- 
ner characteristic snout tubercles of this species and some tooth whorls are shown. Below pyrite mass, elements of the hyobranchial appara- 
tus, the pectoral fins, the pelvic cartilages with two clusters of large tenacular hooks, the clasper mechanism, and a partially articulated 
vertebral column showing peculiar fusions (?) in the pelvic area can be seen. P=Petrodus denticles and L = Listracanthus denticle, not 
associated; area enclosed by dashed line contains a chewed tail fin of the shark Agassizodus, probably on a different bedding plane. 



Fig. 54. Radiograph showing the posterior half of a skeleton of Sibyrhynchus denisoni, PF6506, with part of the tail fin. The clasper 
mechanism is characteristic for this species and permits its identification. Elements circled in dashed lines do not belong to this specimen. 

dimensions, save those of structures parallel to the 
burial plane, are diminished. Upper and lower jaws in 
Sibyrhynchus and Iniopera could have matched in 
length only if one assumes that the mouth was slanted 
at an angle to the horizontal (fig. 58). We have tried 
both an upward and downward slant and have con- 
cluded that an upward slant is the more probable. 

Food. — There is no direct evidence of food associated 
with any of the specimens, but the nature of the denti- 
tion would suggest this to have been a notable predator. 
The tubercles at the tip of the snout and lower jaw no 
doubt protected these important parts very well, but it 
is difficult to appreciate against what hazard. 

Geographical and ecological considerations. — -Sibyr- 
hynchus denisoni is a common species in all the eastern 
localities of the Illinois basin, and very few have so far 
been collected in Iowa or Nebraska. It can be ex- 
pected, however, to occur there as a rare stray, just as 
Iniopteryx rushlaui occurs very rarely in Indiana. A 
large number of Sibyrhynchus specimens occur as gastric 
residues of sharks, which indicates that in spite of its 
tubercles and its sharp teeth it served as prey at least as 
readily as other species of iniopterygians. 

Genus Iniopera 1 , gen. nov. 

Characterization. — Durophagous iniopterygians with 
a double symphyseal whorl (fusion of two adjacent ele- 
ments) in the lower jaw and a single symphyseal in the 
upper; in the lower jaw the third whorl from the 
symphyseal is differentiated as a "canine" whorl; in the 
upper jaw there are two "canine" whorls in positions 3 
and 4 from the symphyseal whorl. Teeth extensively 
fused not merely at base, but for much of the crowns as 
well. Teeth blunt except in juveniles; whorls often 
smooth on functional side; lateral whorls denticulate 
posteriorly along ridge, smooth anteriorly, and medial 
sides of whorls denticulate in an oblique labio-lingual 
row pattern. Snout armored with a small median and 
two large lateral tubercles; lower jaw bears in front two 
large, conical tubercles. The floor of the mouth cavity 
armored with an anterior plate shaped like a three- 
sided pyramid, and a posterior element shaped like a 
pelecypod shell. The roof of the mouth cavity is paved 
with at least two pairs of plates; the larger, posterior 
ones being rectangular in outline, with pointed processes 
antero-medially. All of these plates are tuberculated— 

1 From !'m'on = nape, and pera= leathery pouch. 




Fig. 55. Scapulocoracoid and basipterygium of the pectoral 
fin of Sibyrhynchus denisoni, PF2632. 

the tubercles being mucous membrane denticles fused at 
the base, which becomes fairly thick in large specimens. 

Pectoral fins of presumably adult specimens with 
large, distally pointed sacs, containing a lithified fluid 
similar in appearance to the fossil ink in Liassic di- 
branchiates from Holzmaden. 

Pelvic fins probably relatively small, but clasper 
mechanism consisting on either side of four short ante- 
rior sections followed by an elongated piece and a 
sharply pointed, terminal section consisting of bone (or 
perhaps dentine) and containing a central canal. No 
terminal clasper hooks. 

Type species. — Iniopera richardsoni, n. sp. 

Iniopera richardsoni 1 , sp. nov. 

Type.— FMNH PF2356, tf 1 , skull and pectoral re- 
gion in partial side position. XR:LQ229. 

1 Named for the late Maurice L. Richardson, MD, of Lansing, 
Michigan who generously supported paleontological research at 
Field Museum for many years and who had an active interest in 
the fossils from the black shales of Indiana. 

Horizon and locality. — Logan Quarry shale, Lower 
Wiley cyclothem (Staunton formation), Westphalian C, 

Logan Quarry, level G, NE-#, SW-J4, Sec. 9, 
T16N, R8W, Reserve Township, Parke County, In- 
diana, about 1 :! 4 miles east of West Union (Zangerl 
and Richardson, 1963, fig. 15). 

Referred specimens. — 
Wea shale 

PF6654, d\ articulated, partial skeleton, (W. D. White) 
PF6655, <?, partial skeleton, (W. D. White) 
PF6685, — , small, partial skull, (G. R. Case) 
PF6690, — , gastric residue, (G. R. Case) 
PF6749, — , gastric residue, (G. R. Case) 


PF6656, d 1 , articulated, partial skeleton, (W. D. White) 
PF6699, — , tiny head and shoulder region, (G. R. Case) 
PF7205, d\ articulated juvenile specimen, (W. D. 

PF7204, c? , articulated, partial skeleton, (W. D. White) 
PF7209, d\ articulated partial juvenile skeleton, (W. D. 


PF7210, ?d\ partial skeleton, (W. D. White) 
PF7212, cf , good, partial skeleton, (W. D. White) 
PF7124, d\ good, partial skeleton, (W. D. White) 
PF7185, — , juvenile specimen, incomplete, (W. D. 

Stark shale 

Ft. Calhoun 

PF6692, — , part of skull, (G. R. Case) 

PF6695, — , skull and lower jaw with tooth whorls in 

place; juvenile individual, (G. R. Case") 
PF6697, — , part of skull, (G. R. Case) 



Fig. 56. Tentative reconstruction of the skeleton of Sibyrhynchus denisoni in side view. The proportions of the different parts of the 
skeleton are only approximately correct. Below, pelvic complex of male in ventral view. 



Fig. 57. Discrepancy in the length of the mandible and the 
neurocranium forward of the jaw articulation. The specimen de- 
picted is PF2632, but similar discrepancies have been observed in 
several specimens of Sibyrhynchus and Iniopera. For an explana- 
tion see text and Figure 58. 


Bethel Church 

PF6426, d\ partial skeleton, partly articulated, XR: 
Bethel 3 

PF6443, c? , very juvenile specimen, mostly disarticu- 
lated, XR: Bethel 7 

PF6498, ?d\ good, partial skeleton, small individual; 
XR: Bethel 15 

PF6499, — , gastric residue, XR: Bethel 9 

PF6505, — , disarticulated skeleton, partly very good, 
XR: Bethel 24 

PF6507, — , partial skull, lower jaw, XR: Bethel 25 

PF6512, — , partial skull disarticulated 

PF6526, d\ chewed individual, XR: Bethel 57 

PF6527, d\ partial skeleton, has both pectoral pouches, 
XR: Bethel 17 

PF6528, d\ gastric residue (juvenile), XR: Bethel 19 

PF6530, — , gastric residue, containing possibly two 
specimens of different size, XR: Bethel 18 

PF6533, d\ good partial skeleton, XR: Bethel 35 

PF6534, — , nearly entire, articulated skeleton of juve- 
nile, XR: Bethel 37 

PF6535, ? 9 , fair skeleton, weathered 

PF6553, c? , nearly complete skeleton including skull in 
side position, XR: Bethel 46 

PF6554, d\ good anterior half of skeleton, XR: Bethel 

PF6591, d\ minced specimen, XR: Bethel 41 

Barret Cemetery 
PF6449, — , chewed skull and shoulder, XR: Barret 4 
PF6454, cr\ partial skeleton, XR: Barret 10 
PF6465, — , gastric residue, XR: Barret 13 
PF6550, d\ gastric residue 
PF6561, — , anterior part of skeleton, disturbed, XR: 

Barret 16 
PF6564, — , two specimens (both chewed) on different 

bedding planes; specimen with braincase carries 

number, XR: Barret 19 
PF6612, — , tiny, chewed specimen with good lower 

jaw, XR: Barret 27 

Pit 14 
PF6540, d\ chewed partial skeleton, XR: Pit 14, No. 11 
PF6542, — , disarticulated skull, XR: Pit 14, No. 5 
PF6569, — , minced specimen 

Mecca Quarry Shale 

Mecca Quarry 

PF2807, d\ skull and shoulder, rasp hooks in place; 
Mecca quarry, level B4.1, XR: MQ 34 

PF2825, — , partial skull; Mecca quarry level A3.1, XR: 
MQ 191 

PF2898, — , skull disarticulated, good lower jaws; juve- 
nile, Mecca quarry, level A4.3, XR: MQ 204 

PF2899, — , disarticulated skull, Mecca quarry level 
Bl.l, XR:MQ72, 73 

PF2902, — , gastric residue, Mecca quarry, level A4.4 

PF2905, — , gastric residue, Mecca quarry, level A4.1 
XR: MQ 53 

Fig. 58. Explanation of the discrepancy of the length of the 
mandible and the forward portion of the neurocranium which is 
indicated on the horizontal line. For a full explanation see text. 



Fig. 59. Iniopera richardsoni, PF2356 (holotype). Positive radiograph of specimen approximately in side position (see also fig. 64). 

PF2919, — , gastric residue, pectoral fin pouch, Mecca 
quarry level B2.4 

PF2924, d", gastric residue containing numerous ele- 
ments of this species as well as arm hooks of a ? 
cephalopod; Mecca quarry, level A3.2, XR: MQ 

PF2925, — , gastric residue; Mecca quarry, level A2.2, 
XR: MQ 173 

PF2931, — , good disarticulated specimen, braincase, 
lower jaw; Mecca quarry, level B2.2, XR: MQ 77 

PF2932, — , excellent, disarticulated skull, partial; 
Mecca quarry, level B2.1; XR: MQ 22 

PF2934, — , gastric residue; Mecca quarry, level B1.4; 
XR: MQ 164 

PF2937, — , gastric residue; Mecca quarry, level B1.2 



PF6659, d\ isolated rasp hooks with large star-shaped 

bases; Mecca quarry, level A2.4 
PF6717, cf , gastric residue; Mecca quarry, level Bl.l 
PF6726, — . gastric residue containing Iniopera and 

paleoniscoid remains; Mecca quarry, level Bl.l; 

PF6737, — , gastric residue; Mecca quarry, level A1.3 

PF7115, — , gastric residue containing pectoral fin 
pouch; Mecca quarry, level B2.4 

CL154, cf , anterior half of skeleton, articulated. XR, 
Property of Mr. John Carlson. Recovered from 
lateral extension of Field Museum's Mecca Quarry 

U.S. Highway 41 
PF1021, — , partial skull. XR: Disc. Site 16 

Montgomery Creek 

PF6626, — , good, small lower jaw with tooth whorls in 

PF6624, — , scattered elements. XR: Montgomery 

Creek 4 

Spencer Creek 
PF6625, — , disarticulated skull. XR : Spencer Creek 2 

West Montezuma 

PF6622, <f , anterior two-thirds of an articulated skele- 
ton with pouch fills. XR: Montezuma 13 

PF6630, — , disarticulated specimen 

PF6631, — , disarticulated specimen 

PF6638, — , disarticulated specimen 

PF6640, — , anterior two-thirds of articulated specimen 
with pouch fill 

PF6739, — , part of a cranium. XR: Arketex-2 

Otter Creek 

PF6589, — , disarticulated skeleton with both pouch 
fills. XR: Otter Creek 5 

Chinook Mine 
PF5886, cf, disarticulated skeleton. XR: Chinook 8 
PF5889, — , disarticulated skeleton, XR: Chinook 10 

Logan Quarry shale 

Logan Quarry 

PF2353, — , part of a mandible and ?neurocranium. 

Logan quarry, level G. XR: LQ 275 
PF2359, cf, large part of excellent skeleton, Logan 

quarry, level J. XR: LQ 92 

PF2593, cf , disarticulated skeleton, Logan quarry, level 

Characterization. — Same as for genus. 

Description. — Iniopera richardsoni is a common, 
highly characteristic element of the Mecca fauna. Its 

Fig. 60. Much enlarged (negative) radiograph of the peculiar, 
radio-opaque substance within the pouch fills of Iniopera richard- 
soni, PF2356 (see fig. 59). 

skeleton is the most highly sclerotized of all inioptery- 
gians, the dentition being durophagous and thus rela- 
tively massive, and the mouth plates and snout tuber- 
cles relatively thick; the end sections of the claspers are 
sclerotized and there is evidence of dermal armor in the 
form of pavements of denticles in the head region and 
scattered ones in the form of little "snowflake" denticles 
over part of the body. 

A most peculiar feature of this form is the presence 
of a pair of mostly membranous pouches (fig. 59), asso- 
ciated with the pectoral fins, which contain a highly 
organic, lithified substance that breaks with conchoidal 
fracture and resembles somewhat the lithified ink in the 
ink sacs of Jurassic dibranchiates. Not every specimen 
shows these pouches, and their size appears to have little 
to do with the size of the animal (except that small 
individuals never show them). It is thus probable that 
the size of the pouches depends on the amount of sub- 
stance (probably a fluid) that they contained at the time 
of death, not on the age of the individual. So far, all 
specimens that show pouches are males. Furthermore, 
the pouches of the type specimen PF2356 each contain a 
fibrous patch of substance within the pouch-fill that is 
highly radio-opaque as seen on X-ray film, indicating 























Fig. 62. Iniopera richardsoni, PF6622. Drawing of the head region made from enlarged stereo radiographs. 

that it contains an element of relatively high atomic 
weight (fig. 60). We have no idea what this material 
might represent, why it seems to be concentrated within 
the substance of the pouch-fill, or why it should be 
fibrous in structure. 1 The nature of these organs is, of 
course, likewise a matter of speculation at this time. 
They might be analogues of the ink sacs of dibranchi- 
ates; they might be poison glands or even accessory 
male sex glands. Less probable, though not impossible 
is the notion that they served as incubators for the eggs, 
perhaps carried by the males. The idea that they might 
represent parasitic infestations seems the least likely 


Several specimens (e.g., PF2359, PF6622), show the 
braincase in dorso- ventral position (figs. 61, 62). In all 
cases one can distinguish a dorsal portion which formed 
the roof and sides of the brain cavity, contained the or- 
bits and enclosed the nasal cavities, though the latter 
two features are never distinctly seen. In PF2359 there 
seems to be a broad depression in the snout region of the 
skull roof (fig. 61) resembling somewhat the cavum 
precerebrale of sharks (see, for example, Smith, 1937, 
pi. 1). The ventral portion of the neurocranium con- 
sists, as in other genera of this order, of a median 
longitudinal plate to which the vertebral column at- 
taches posteriorly, transverse ridges that extend to the 
postero-lateral corners of the neurocranium and a little 

1 Chemical analysis is contemplated as soon as additional 
specimens with this feature become available. 

more dorsal (though beneath the dorsal roof), the paired 
sheets of calcined cartilage (? posterior parts of the pa- 
latoquadrates) that are attached to the postero-lateral 
corners of the neurocranium and to the medio-ventral 
plate, and terminate anteriorly in the articular facettes 
for the fused Meckel's cartilages (fig. 61). The for- 
ward portions of the palatoquadrates are so intimately 
united with the neurocranium that their presence can 


Fig. 63. Camera lucida drawing of a patch of dermal denticles 
that form a pavement presumably on the dorsal (or ventral) side 
of the head of Iniopera richardsoni (PF7129). 

Fig. 64. Iniopera richardsoni, PF2356 (holotype). Drawing made from enlarged stereo radiographs (see fig. 59). 




only be surmised. We assume that they form the tooth- 
bearing parts of the upper jaw. 

The snout is armored in front by a blunt medial and 
two stout, lateral tubercles; additional minor tubercles 
may be present elsewhere on the skull and there is evi- 
dence that small dermal denticles may have dotted the 
skin of the head and may even have formed a pavement 
over the dorsal or ventral portion of the head region 
(fig. 63). The Meckel's cartilages are fused at the 
symphysis which forms a fairly broad shelf. At the 
antero-lateral corners there are two notably pointed 
tubercles (figs. 64, 65). 

Fig. 65. Snout tubercles, dentition, and mouth plates of 
Iniopera richardsoni, PF2356 (holotype). Drawing made from 
greatly enlarged stereo radiographs. Compare with Figure 64. 

The dentition is durophagous. It consists of fairly 
massive tooth whorls in which the individual tooth 
crowns are short and relatively blunt in adult individ- 
uals. Anteriorly many tooth whorls are devoid of den- 
ticles and we assume that they have been worn off (fig. 
65) . A longitudinal section through a tooth whorl of an 
adult specimen shows that the individual teeth are very 
extensively fused to one another, not merely at their 
bases, but along the sides of the crowns (fig. 66). In 
very small individuals the teeth composing each whorl 
are much larger relative to the size of the whorl and 
more acutely pointed than in the adult condition so that 
individual tooth whorls of young individuals may be 
mistaken for those of Inioxyele or even Sibyrhynchus. 

The lateral tooth whorls are particularly interesting, 
because they seem to be not merely fusions of teeth be- 
longing to single tooth families, but additionally of 
adjacent tooth families. This might explain why their 
lingual surfaces are covered with teeth in oblique, labio- 
lingual rows (fig. 67). 

The upper dentition consists of a symphyseal whorl, 
followed by seven pairs of whorls. The third and fourth 
pairs are differentiated as "canine" whorls. In the 
lower dentition the symphyseal element consisting of 
the fusion of a pair of whorls is clearly seen in a 
specimen in which the whorls are viewed from the un- 
derside (fig. 68). There are six pairs of whorls in the 

lower jaw. The third pair is differentiated as "canine." 
The anterior lower tooth whorls seem to be much 
broader and stouter than the opposing upper whorls 
(fig. 69). 

The mouth cavity is armored with rather massive 
plates in the adult condition. As in Sibyrhynchus, these 
plates are the product of basal fusion of pavements of 
mucous membrane denticles that become dull upon 
wear and may disappear entirely on the most heavily 
worn parts of the plates (fig. 67). The shapes of these 
plates are characteristic for the genus. On the floor of 
the mouth (resting on elements of the hyobranchial 
skeleton) there is an anterior, triangular plate shaped 
like a three-sided pyramid whose posterior side is a 
little smaller than the two antero-lateral sides. Behind 
this plate there is another, shaped like a pelecypod shell 
with the hinge side facing forward (fig. 70). On the 
palate there are two rectangular plates, each bearing 
antero-medially a strong projection. These plates are 
also three-sided pyramidal, the postero-lateral side 
being far and away the largest. A second pair of much 
smaller plates is located immediately in front of the 
larger pair, fitting into the notches produced by the 
forward processes of the larger plates (fig. 71). In addi- 
tion, there appear to be even smaller plates whose 
exact position remains to be determined (fig. 70). 

Fig. 66. Camera lucida drawing of a tooth whorl of Iniopera 
richardsoni, PF6630, that had been broken lengthwise. Note ex- 
tensive fusion of denticles. 

Hyobranchial apparatus: 

The three elements, a, b, and c, of Figure 72 are 
very often seen isolated but associated with specimens 
of Iniopera richardsoni. Piece "a" is almost always 
seen in the position shown and is always asymmetrical, 
never paired. We thus assume that it is an unpaired, 
sagittal element with the sagittal plane located parallel 
to the paper on which it is drawn. Only very rarely are 
elements "b" and "c" associated with a symmetrical 
piece to which the three-sided pyramidal mouth plate 
(see above) is attached (fig. 73). As the type specimen 
clearly shows, the symmetrical, three-sided, pyramidal 
mouth plate was located in life on the floor of the 
mouth cavity. We, therefore, interpret the element 
"a" as the anteriormost element of the copula, a gloss- 
ohyal. Element "b" corresponds very well with the 
second copula cartilage described in Sibyrhynchus (p. 






-W-'K •i" <\ vf w *"- Jf- 

!•?>**?**?•*. i*"* 1 

;.;:;.;j^.j. ;.;..!; 



Fig. 67. Iniopteryx richardsoni, PF2593. Photograph of a polysulfide rubber cast (Smoothon) of part of the dentition, snout tubercles 
and mouth plates. 


Fig. 68. Camera lucida drawing of the lower jaw of Iniopera 
richardsoni, PF 6561, in which the undersides (pulp cavity sides) 
of the tooth whorls are visible. 

Fig. 69. Diagrammatic illustration of the dentition of Ini- 
opera richardsoni. 



Fig. 70. Positive radiograph of a portion of the skeleton of Iniopera richardsoni, PF2932. hb, hyobranchial elements; p, palatal plates; 
s, scapulocoracoid; M, Meckels cartilages fused at symphysis. Elements enclosed in dashed line do not belong to the specimen. 

38) where it is somewhat stouter than in Iniopera. 
Element "c" is also seen in Sibyrhynchus and is prob- 
ably a ceratohyal (see p. 39). 

Shoulder girdle and pectoral fin: 

The shoulder girdle is a fairly massive set of cartil- 
ages with well-developed articular heads for the basip- 
terygial articulation. In PF2359 (fig. 61) it looks as if 
the articular heads were at the dorsal ends of the 
scapulocoracoids, but this is not the case; the portions 
above the heads have been folded under and are thus 
mostly hidden (shadowed on the radiograph). The 
shape of the basipterygium is clearly seen in Figure 61. 
It is provided, at the wider end, with a pronounced ar- 
ticular pan for its articulation with the shoulder girdle, 
and a strongly protruding joint head for the articula- 
tion of the first (anterior-most) finray. The type speci- 
men is by far the best for the description of the pectoral 
fins. These consist of about eight cartilaginous rays, 
the first of which is much enlarged and perhaps (though 

not certainly) segmented. It bears rasphooks of the 
same general construction as in Sibyrhynchus, Promex- 
yele, and Iniozyele, but not in very large numbers. In 
contrast to other iniopterygians, the first ray is not the 
longest. Instead the third ray appears to be the long- 
est (fig. 64) . The fourth, fifth, and sixth rays seem to be 
associated with the pouch. Their curvature fits closely 
the curvature of the pouch, and they may have served 
to reinforce its membranous wall. 1 

1 We have interpreted the highly organic, conchoidally frac- 
turing bodies associated with the pectoral fins of this fish (fig. 64) 
as lithified contents of membranous pouches because these bodies 
are three dimensionally preserved with sharp, smooth outlines. 
They are enclosed neither in calcified cartilage nor in any other 
kind of sclerotized tissue, but some of the fin rays were clearly ap- 
plied to the outside of these bodies. Since it is not reasonable to 
suppose that these bodies consisted of a solid substance during the 
life of the animal, but rather a fluid of some sort, one is forced to 
postulate a membrane that would have contained the fluid (or gel) 
after death. Zangerl and Richardson (1963) have postulated, on 
different grounds, extremely rapid deposition of the black muds in 
which these organisms became buried. The present occurrence 
strongly supports that conclusion, because bacterial decomposi- 
tion of a membrane in water of 21° C. (or more) is a matter of a 
very few days. 




Fig. 71. Palatal plates of Iniopera richardsoni, PF2899, pre- 
served in association. 

In PF6622 (fig. 74), in which both pouches are pres 
ent, but where the pectoral fins are not very well pre" 
served, the pouches are much smaller than in the type 
specimen and behind their posterior ends there are two 
aggregations of fishhook-shaped denticles that look 
rather conspicuously like clasperhooks. When this 
specimen was collected, it was split through the plane 
of the fossil, dividing it into plate and counterplate. 
The split went through the pouches to expose their sub- 
stance and this was enclosed, all around, by calcified 
cartilage. Hence we cannot be entirely sure that the 
pouch-fills in PF6622 are the same structures as those 
in the type specimen PF2356, yet these specimens 
surely belong to the same species. The differences 
noted may not be differences at all: fishhook denticles 
may have been present behind the pouches in the type 
specimen where the shale slab is so broken that the 
hooks may be on the missing piece of the specimen, and 

the split through the pouches of PF6622 may have gone 
across supporting finrays on both sides. The situation 
obviously requires clarification by additional specimens. 

Vertebral column and unpaired fins: 

The vertebral column is organized much as in other 
iniopterygians. In PF2359 we see the anterior portion 
of the column in ventral view. This consists of two 
columns of ventral arcualia (fig. 61) ; farther back the 
dorsal arch pieces are more clearly seen in this specimen. 
In none of the presently available specimens is the en- 
tire vertebral column preserved in such a way as to per- 
mit detailed description. In PF6656 there is a partial 
tail fin which shows in essence the same construction as 

Fig. 72. Hyobranehial apparatus of Iniopera richardsoni. 

Fig. 73. Hyobranehial apparatus with superposed plates of 
Iniopera richardsoni, based on PF6638. 

in Iniopteryx. Both dorsal and ventral finrays in this 
individual are slanted obliquely backwards, a condition 
that is also occasionally observed in Iniopteryx. We 
assume that Iniopera possessed a dorsal fin, though none 
of the specimens show the structure in situ. 

Pelvics and clasper mechanism: 

The pelvic cartilages are slender, relatively straight, 
and distally slightly enlarged elements. The basiptery- 
gia are triangular as in other iniopterygians. In the 
male specimen, PF6656 (fig. 75), they seem to be rel- 
atively smaller than in the presumed female, PF6535. 
but this may be due to less perfect preservation. 

The clasper apparatus of this species is very dis- 
tinctive. It is seen in PF6656 and PF7124 (figs. 75, 
76). The proximal portion of each clasper consists of 
about four cartilaginous segments each about as long 
as wide (in the present flattened condition). This is 

Fig. 74. Positive radiograph of Iniopera richardsoni, PF6622. t, tenacular hooks; ch, clasper hooks; pf, pouch fill. P=Petrodus\ieT\ti- 
cles in other bedding planes. 




10 mm 

Fig. 75. Camera lucida drawing of the pelvic complex of Iniopera richardsoni, PF6656. 
bone or dentine; L, lumen of central canal. 

Abbreviations: cc, calcified cartilage; ?B, 

followed by an elongated cartilage rod about as long as 
the four proximal elements taken together; the distal 
element is also elongated, tapering to a point. But it 
consists, except for its proximal end, of a material that 
resembles bone or dentine on the break. Because it 
consists of a dense, sclerotized tissue, this section of the 
clasper shows the central canal (fig. 75), which we as- 
sume was also present in the cartilage rods, but is not 
seen there because calcified cartilage collapses during 
bacterial decomposition. No clasper hooks were noted 
at the distal ends of these sclerotized clasper segments. 

Dermal denticles: 

It was mentioned above that there are dermal ele- 
ments distributed about the head region, sometimes 

apparently even forming patches of pavements (fig. 
63). Many specimens, furthermore, show a sprinkling 
of dermal denticles resembling snowflakes in the region 
of the abdomen; their number is not very great and it 
is possible that they lined the mid-dorsal or mid-ventral 
lines of the body. Not infrequently two such "snow- 
flakes" are fused into a single element (fig. 77). Inio- 
pera is thus the only iniopterygian in which dermal den- 
ticles occur in the skin back of the head region. 

Appearance in life: 

Iniopera richardsoni probably presented a variety of 
sights to the Pennsylvanian observer, depending on 
whether its pouches were filled, partially filled or empty. 
We have attempted a reconstruction of the skeleton 



*-. / 

Fig. 76. Reconstruction of the pelvic complex of Iniopera richardsoni, based on several specimens. 

(fig. 78) but it must be remembered that no whole skele- 
tons are known, hence the proportions of the parts to 
one another may not be entirely correct. 

Since the questions as to the nature and function of 
the pouches remains unresolved (see above), it is not 
yet possible to place this animal meaningfully into the 
flotant environment (Zangerl and Richardson, 1963) 
which it inhabited, along with all other iniopterygians. 


To judge by the dentition this animal was probably 
able to avail itself of a variety of foods besides crusta- 
ceans such as Concavicaris sinuata which apparently 
was in plentiful supply in the flotant environment. The 

fact that the tooth whorls and mouth plates tend to be 
worn does not necessarily indicate that this fish ate 
hard-shelled prey; more likely it fed on whatever foods 
happened to be available (as do modern Eagle rays) and 
this almost certainly included leftovers produced by 
the large numbers of sharks that inhabited this environ- 
ment, namely partly eaten sharks, iniopterygians, 
palaeoniscoids, and acanthodians. The calcified skele- 
tons of these fishes might have provided the abrasive 
that ground down the tooth whorls and mouthplates of 
Iniopera. Since the bottom mud of the flotant environ- 
ment was probably toxic (H 2 S), it contained no infauna 
and hence none of the inhabitants of this habitat can^be 
assumed to have been bottom feeders. 

Fig. 77. Photograph of dermal denticles ("snowflakes") of Iniopera richardsoni, PF6535. 






Fig. 78. Tentative reconstruction of the skeleton of Iniopera richardsoni in lateral view. The proportions of the different parts of 
the skeleton are only approximately correct. 

Geographic and stratigraphic occurrence: 

Iniopera richardsoni is a very common member of 
the Mecca fauna of the Illinois basin and is not at all 
rare in the western localities. For reasons not apparent, 
the majority of the western specimens are juveniles and 
so far no specimens have been found in the western 
localities that show the pouches. The most likely rea- 
son for this is the extreme rarity of adult skeletons in 
those localities. I. richardsoni has been collected in 
most of the localities shown on Figure 1 and may be 
expected in any black shale horizon in which inioptery- 
gians occur. 

Genus Inioxyele 1 , gen. nov. 

Characterization. — Iniopterygians with sharp- 
toothed dentition, consisting in the lower jaw of a sym- 
physeal and four pairs of whorls; the "canine" whorl 
being the second from the symphyseal whorl. Roof 
and floor plates of the mouth cavity present (but their 
shapes remain to be determined). One double ten- 
acular hook on each side, located on the basipterygium. 
Each clasper consists of an elongated proximal element, 
a series of about four short pieces and an elongated 
terminal rod that tapers to a point. Tiny clasper hooks 
present at distal end of clasper apparatus. 

Type species. — Inioxyele whitei, n. sp. 

Inioxyele whitei, 2 n. sp. 

Type.— FMNH PF6651, d\ large portion of a skele- 
ton divided on plate and counterplate, lacking the tail 
and much of the vertebral column. 

1 From inion= nape, and x#e/e=rasp. 

1 The species is named after Mr. W. D. White who is a most 
indefatigable collector of iniopterygians and other fossils in the 
black shale localities around Omaha, Nebraska. 

Horizon and locality. — Queen Hill shale, Lecompton 
formation, Shawnee group, Virgil series, Stephanian 
A, Pennsylvanian 

Ace Hill Quarry, Plattsmouth, Nebraska. Col- 
lected by W. D. White of Omaha, Nebraska 

Additional material. — The present collection of 
iniopterygian material contains a considerable number 
of specimens either of very young individuals, or of 
badly disarranged partial skeletons some of which may 
well belong to this species. At this stage of our knowl- 
edge of the iniopterygians, however, it is not possible 
to identify with confidence any of these specimens to 
the species presently recognized. 

Characterization. — As for the genus. 

Description. — Unfortunately, the description has to 
be based on one individual, the holotype (fig. 79). 
This skeleton shows a number of features of the denti- 
tion and the clasper mechanism, sufficiently distinctive 
to rule out the possibility of its being an abnormal in- 
dividual of one of the other species here defined. We 
believe that additional specimens will show that this 
form is as distinctive as are the other species here 

As is most often the case with specimens from the 
black shales, this individual was discovered by splitting 
a piece of shale, and, as also happens most often, the 
split divided the skeleton on plate and counterplate. 
making it very difficult to study. The tooth whorls 
and the mouth plates were torn apart, but fortunately 
the tooth whorls of the lower jaw, though somewhat 
broken, display the original relationships to one an- 
other (fig. 80). The tooth whorls are provided with 
well-separated and sharply pointed tooth crowns as in 
Sibyrhynchus; the "canine" whorl is the second whorl 
from the symphyseal one. not the third, as in Sibyrhyn- 
chus. Also there is a very considerable size difference 

I J '% IJ\ 

Fig. 79. Inioxyele whitei, PF6651 (holotype). Camera lucida drawing. 




Fig. 80. Camera lucida drawing of the dentition as seen on 
the plate. Inioxyele whitei, PF6651 (holotype). 

between M-l and the "canine" M-2, a difference that 
is much less pronounced between M-2 and the "canine" 
M-3 of Sibyrhynchus (fig. 49). The dentition of the 
lower jaw of Inioxyele whitei consists of a symphyseal 
whorl and four pairs of whorls. Unfortunately, very 
little can be said about the tooth crowns, since most of 
them are broken off (fig. 80). On the counterplate 
(fig. 81), in addition to parts of the lower jaw dentition, 
there are a number of tooth whorls of the upper denti- 
tion. These whorls are not preserved in situ and their 
identification as to their position within the dentition is 
thus somewhat questionable. The whorl with the 
largest teeth, in the upper left corner of the illustra- 
tion, is probably the "canine;" its mate (with broken 
tooth crowns) lies nearby. 

The isolated whorl with 13 tooth crowns showing is 
either P-4 or P-5, P-4 being the more likely because of 
the notable curvature of this whorl. If the above 
interpretations are correct the dentition of Inioxyele 
whitei (fig. 82) differs considerably from that of Sibyr- 
hynchus denisoni, even though the individual tooth 
whorls are very similar. 

The mouth cavity of this fish was armored by plates 
much as in Sibyrhynchus and Iniopera, but at this time 
their shapes cannot be made out, nor their arrangement 
on the floor or the roof of the mouth cavity. 

The pectoral fins of the male had a somewhat en- 
larged first ray which bore 60-80 rasp hooks with large 
bases that diminish in size distad. These rasp hooks 
are very similar to those of Promexyele (fig. 37). The 

Fig. 81. Camera lucida drawing of the dentition as seen on 
the counterplate. Inioxyele whitei, PF6651 (holotype). 

vertebral column has almost completely disintegrated; 
what is visible suggests that the column was organized 
much as in other iniopterygians. 

The pelvic elements are slender, slightly curved, 
distally somewhat expanded cartilages (fig. 79). At- 
tached to them were the triangular basipterygia of the 
pelvic fins. Tenacular hooks, single or double on each 
side, apparently were located on the basipterygia (fig. 

The clasper mechanism consists on each side of a 
longish proximal rod, followed by four or five short seg- 
ments and ends in another elongated distally tapering 



Fig. 82. Reconstruction of the dentition of Inioxyele whitei. 




Fig. 83. Reconstruction of the pelvic complex of the male of Inioxyele whitei. 

cartilage rod (fig. 79, 83). The very tip of the latter 
may or may not have consisted of a sclerotized tissue 
similar to that in Iniopera (p. 56). Near one of these 
terminal clasper pieces there is a small accumulation of 

very curious, tiny denticles, no two of which appear to 
be alike (fig. 79). We interpret these as terminal 
clasper hooks that have the shape of tiny hands with 
variable numbers of fingers (fig. 79) . 


The seven species of fossil fishes described above 
conform in their structural organization to a mutual 
plan: the skeletons consist of calcified cartilage; the 
skull is unquestionably autostylic; the pectoral fins are 
enlarged and attached to the shoulder girdle near the 
dorsal end, thus extending from the body near the 
"nape" of the neck; the gill region was evidently cov- 
ered by an opercular flap ; the tail region is slender and 
the tail fin is more or less circular in side view; the males 
have species-characteristic, elaborate clasper mechan- 
isms and tenacular hooks ventral to the pelvic cartilages 
or on the basipterygia of the pelvic fins, and a variety 
of denticles attached to the enlarged first pectoral fin 
ray; the dentition varies from simple, conical denticles 
arranged in labio-lingual tooth families, to tooth whorls, 
fusions of the elements of single tooth families, to com- 
plex dental plates probably involving the fusion of 
several adjacent tooth whorls; the mouth cavity, both 
roof and floor, may be armored with plates formed by 
the fusion of patches of mucous membrane denticles; 
the skin is usually naked, devoid of dermal denticles, 
except about the snout, and, in one genus, where there 
are patches of modified dermal denticles about the 
head and individual ones in the region of the thorax; 
the spiral membrane inside of the spiral intestine per- 
formed at least 14 turns (observed in Iniopteryx rush- 
laui only). 

This combination of features leaves no doubt but 
that their bearers are chondrichthyans. Moreover, the 
character assemblage includes typical aspects of both 
chondrichthyan subclasses, the Elasmobranchii and the 
(chimeraeroid) Holocephali 1 as follows: 

Elasmobranch structural affitiites: the dentition in 
the more generalized genera; the large number of turns 
of the spiral membrane of the spiral intestine; the ter- 
minal mouth opening; the cartilaginous finrays of the 
pectoral and tail fins which extend to the margins of 
these fins (the last two characters being typical of 
Paleozoic elasmobranchs). 

Chimaeroid structural affinities: the autostylic jaw 
suspension; a cartilage ray - supported opercular flap; 
the slender tail (though not the tail fin) ; the presence of 

1 The suborder Chimaeroidei, as here understood, includes 
only the families Squalorajidae, Myriacanthidae, Chimaeropsidae, 
Acanthorhinidae, Chimaeridae, Rhinochimaeridae, and Cal- 

tenacular hooks; the general nakedness of the skin; the 
tendency toward dental fusions'-; the elaborate clasper 
mechanisms in males; the overall bizarre appearance 
of the animals. 

The combination of elasmobranch and chimaeroid 
features makes the Iniopterygia structural interme- 
diates between the two compared groups, not, how- 
ever, phylogenetic intermediates. 

Both the iniopterygians and the chimaeroid holo- 
cephalians are structurally compact and clearly circum- 
scribed groups. The morphological distinctions be- 
tween them represent different structural solutions 
to similar problems, as shown in Table 1. 

Table 1 suggests a sister group relationship, sensu 
Hennig (1966), between the two groups, a conclusion 
that necessitates the postulation that relatives of the 
chimaeroid holocephalians existed in Pennsylvanian 
time. The question as to whether any of the known 
Paleozoic chondrichthyans could possibly be regarded 
as relatives of the chimaeroids was most recently ana- 
lyzed by Patterson (1965). His arguments strongly 
pointed toward Helodus simplex Agassiz, though a num- 
ber of features of this fish seemed to militate against 
such an assignment — for example, the selachian type of 
dentition with numerous tooth families along the jaws 
and several teeth in each family; the presence of a dor- 
sal spine of peculiar microscopic anatomy (but with one 
chimaeroid structural detail) ; and the absence of der- 
mal armor on the head. 

With the discovery of the iniopterygians the ques- 
tion of the systematic position of Helodus becomes once 
more acute. Clearly, the shark-like dentition of this 
fish is no longer an obstacle to its being considered as a 
primitive chimaeroid, nor is the absence of dermal head 
armor. The matter of the dorsal spine is somewhat in- 
conclusive inasmuch as the section (Patterson, 1965, 
pi. 22, fig. 48) was probably ground from the lower part 
of the spine where it accomodated the basal cartilage 
of the fin, while the section through the Chimaera sp. 
spine (loc. cit., fig. 45) probably was made from a more 
distal portion of the structure. Since the microscopic 
anatomy of chondrichthyan fin spines is notably com- 

- The complex microscopic anatomy of the dental plates of 
chimaeroids suggests that these structures are the result of fusion 
of more primitive dental elements, though embryological work has 
furnished no hint of such a history. 






Paired, denticulated, pectoral fin rasps 


Mucous membrane denticles in mouth cavity 
with tendency toward fusion into plates 

Sensory canals probably not lined with dermal 

Trend toward fusion of dentition teeth belong- 
ing to tooth families to form tooth whorls, and 
of adjacent tooth whorls 

A single dorsal fin without a spine 

Tail fin circular in side view 

No fusion of the anterior vertebral arches 

Chimaeroid Holocephalia 
Unpaired, denticulated head claspers 

No mucous membrane denticles 

Sensory canals lined with dermal denticles 

Mode of fusion of dentition teeth to form dental 
plates not known, but almost certainly differ- 
ent from that of iniopterygians 

Two dorsal fins, first with a spine 

Tail fin tapering to a point 

Fusion of anterior vertebral arches (synarcual) 
in connection with the anchoring to the dorsal 

plex 1 and not yet adequately understood, the differ- 
ences noted by Patterson do not seem to weigh heavily 
at this time. By contrast, the similarities between the 
chimaeroid skeleton and that of Helodus as summarized 
by Patterson (1965) are most impressive, and we can 
find no convincing argument that would preclude the 
assignment of Helodus to the order Chimerida. 

Patterson (1965) included among the Chimaeri- 
formes not only the chimaeroids proper, but also the 
menaspoids, represented by the Permian genus Menas- 
pis and the Carboniferous Deltoptychius. Bendix-Alm- 
green (1971) re-examined the best-preserved skeletons 
of Menaspis and came to a different interpretation of 
its morphology than did Patterson (1965, 1968). As a 
consequence of this, Bendix-Almgreen has ruled out 
the possibility of a close phylogenetic relationship be- 
tween Menaspis and the chimaeroids. In view of the 
fact that Menapsis has nothing in common with the 
iniopterygians, we are inclined to agree with the views 
of Bendix-Almgreen. 

Among the Holocephali Patterson (1965) not only 
included the Chimaeriformes (including the menaspoids 
and, incerlae sedis, the cochliodonts) , but, in addition, 
a host of groups that are very poorly known at present: 
the copodonts, the psammodonts, the petalodonts, as 
well as the helodontids, the edestids, and the chon- 

There is no gain in speculating on the possible affi- 
nities of the above groups that are known only from 
teeth. The edestids, to judge from such genera as 
Fadenia, Agassizodus-, and Ornithoprion , are specialized 

1 See, for example, Peyer (1946) and Markert (1896) where the 
complexity of the developing Acanthias spine is further compli- 
cated by the author's misorientation of his sections. Compare 
Markert, 1896, pi. 49, fig. 28, where the anterior face of the spine 
(right side of picture) is erroneously taken as the posterior side 
thus confusing some of the structures, with pi. 48, fig. 21, where 
the orientation is correct. 

2 Much material of this genus is at hand, but not yet described. 

elasmobranchs with a tendency toward reduction (not 
demonstrated in Fadenia) of the palatoquadrates. 

Chondrenchelys problematica from the lower Car- 
boniferous of Scotland stands at the present almost 
completely isolated among chondrichthyans. The dif- 
ferentiation of its median fins has no parallel among 
any other forms, and its biserial pectoral fins occur only 
in pleuracanth sharks, none of which have large, flat 
tooth plates. The skull is thought to be autostylic, 
since no separate palatoquadrate could be detected. 
However, there are not many specimens and no isolated 
neurocrania to establish this point beyond doubt. 3 
Only the vertebral column with its rings, presumably 
calcifications in the sheath of the notochord, resembles 
the chimaeroids. In the absence of any other chimae- 
roid characters, we prefer to place Chondrenchelys, in- 
cerlae sedis, among the elasmobranchs. 

The present analysis thus results in the conclusion 
that the subclass Holocephali contains only two orders, 
the Iniopterygia as defined above, and the Chimaerida 
with the suborders Helodontoidei and Chimaeroidei. 

The question of the phylogenetic relationships of 
the holocephalians not only occupied Patterson (1965), 
but more recently Stahl (1967) who approached the 
problem prmarily (though not exclusively) with mor- 
phological arguments based on modern chimaeroids and 
elasmobranchs. Throughout the analysis Stahl care- 
fully notes the fact that the numerous similarities that 
exist in the anatomical makeup of elasmobranchs and 
chimaeroids may not be the result of the descent of one 
group from the other but rather a reflection of primitive 
features inherited by both groups from their respective 
ancestors. In the case of soft anatomy, questions of 
this sort can, unfortunately, rarely be resolved by the 
fossil record. Stahl makes the valid point, however, 

3 Skulls consisting of prismatic, calcified cartilage rarely show 
useful anatomical detail after collapse due to bacterial degradation 
prior to fossilization. 



that the anatomical similarities between extant holo- 
cephalians and selachians set both groups apart from 
the bony fishes and suggests that they shared a com- 
mon ancestor among placoderm or even preplacoderm 
fishes. In the end Stahl concludes that while "the 
specific group of placoderms from which sharks origi- 
nated is unknown, the ptyctodonts may represent the 
root of the holocephalian line." 

The discovery of the iniopterygians sheds further 
light on this question. For one thing, the dentition is 
typically elasmobranch in Iniopteryx and Promexyele 
and a dentition of this sort is not known among placo- 
derms. Iniopterygians also lack bony armor about the 
head, and bone, as a tissue, is only associated with the 
bases of denticles, much as in the shark Ornithoprion . 
These features alone make it unnecessary to search for 
an ancestor of the holocephalians among the placo- 

The earliest evidence of elasmobranchs in the fossil 
record, about the middle of the Devonian period, con- 
sists of compound scales, in principle similar to the 
compound scales of later Paleozoic forms. The earliest 
elasmobranchs therefore appear to have already dis- 
played the characteristic selachian denticulation of the 
skin which in later Paleozoic forms consisted of simple 
lepidomoria on the ventral parts of the skin and of 
progressively more complex aggregations of lepidomoria 
(complex scales) from the flanks to the dorsum of the 
hide. Since differentiated shark teeth are not associated 
with the earliest scales, it seems probable that the sto- 
modaeum was covered with small, simple, conical den- 
ticles, not much different from the shagreen of the 
underside of the animal. This clearly seems to be close 
to the primitive condition for the chondrichthyans 
whose ancestors, in all likelihood, never possessed 
heavy, dermal armor, but instead had an even spread 
of lepidomorial denticles over the entire surface of the 
skin and the stomodaeum. Both the elasmobranchs 

and the holocephalians (as here defined: Iniopterygia 
plus Chimaerida) probably evolved from such a gen- 
eralized chondrichthyan stock, and represent at the 
present state of our knowledge, sister groups, sensu 
Hennig (1966). 

The systematic grouping of the chondrichthyans as 
suggested by the new evidence may thus be summarized 
as follows: 

Class Chondrichthyes 
Subclass Elasmobranchii 
Subclass Holocephali 
Order Iniopterygia 

Family Iniopterygidae 
Family Sibyrhynchidae 
Order Chimaerida 

Suborder Helodontoidei 
Family Helodontidae 
Suborder Chimaeroidei 
Family Squalorajidae 
Family Myriacanthidae 
Family Chimaeropsidae 
Family Acanthorhinidae 
Family Chimaeridae 
Family Rhinochimaeridae 
Family Callorhynchidae 

In view of the discovery, in recent years, of new 
Paleozoic fish faunas that include much unstudied 
chondrichthyan material, we may confidently look for- 
ward to a much better understanding of the above- 
mentioned relationships as these new materials are de- 
scribed. Moreover, the fact that it is still possible to 
discover whole groups of vertebrates that have escaped 
our notice should once again focus attention on the 
probability that the fossil record is far from adequately 


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